American Projectiles and Explosives - Navy Rockets (Part 4)

American Projectiles and Explosives

Navy Rockets






7.2-inch H.E. "Mouse Trap" and 2.5-inch Practice

No picture available

Overall length: 38.6 inches

Head length: 19 inches

Head weight: 17.9 pounds

Wall thickness: 0.2 inches

Motor length: 15.9 inches

Motor diameter: 2.25 inches

Motor weight: 8.1 pounds

Tail width: 7 inches

Filler Weight (TNT): 31 pounds

Total weight: 65 pounds

General: This rocket was designed for use by patrol vessels against submarines.  The most common installation consists of two four-rail Launchers Mk 20, with a fixed elevation of 48 degrees, mounted on the fore deck with firing controlled from the bridge.


Head: The projectile consists of a flat-nosed head with a conical tail fairing and parallel sides.  The adapter and fuze thread into the nose, and the motor unit threads into the base.


Motor: The Motor Unit Mk 3 contains a long single pellet of smokeless powder which, when ignited by a black-powder primer fired by an electric squib, burns at a pressure of 1,000 to 2,500 pounds per square inch.  The gases are forced out aft through the nozzle in the rear end of the motor tube.  The burning continues for 0.2 to 0.7 seconds, during which time the missile travels about 30 feet.  At this point, propulsion ceases and the projectile is free in flight.  This projector charge is intended for use on the 7.2-inch Rocket Launchers Mk 20, Mk 21, or Mk 22.

Tail: A steel tube attached to the head by a threaded joint has fins with two circular drums attached to the after end.  The vanes have a 10-degree twist to give a slow rotation and prevent ruddering.  The two vane-support drums also act as contact rings, the wiring from the electric squib passing from the primer after to the two rings which serve as firing contacts.


Remarks: When Torpex is used, the weight is increased by approximately 2.5 pounds.

The 2.5-inch sub-caliber rocket, consisting of the 1.25-inch Motor Mk 1 and 2.5-inch Head Mk 1, is a miniature of the regular rocket and is used in practice.  The motor contains a single tubular powder grain, an igniter, and lead wires.  The tail fins, supported by a shroud, are offset five degrees to impart some rotation to the round, to improve underwater travel.  The Head Mk 1 has a cavity for a shotgun shell; the Head Mod 2 Mk 1 is solid.

The Fuzes Mk 131 and Mk 140 are replaced by the Mk 156 in service rounds.

7.2-inch D.R., also T37 and T38

(Head Mk 10)

Overall length: 35 inches

Motor diameter: 2.25 inches

C-2 Explosive: 33 pounds

Loaded weight: 60 pounds

Maximum range: 275 yards

Motor: 2.25-inch Mk 3

Fuzes:

-Head Mk 5: Nose Fuze Mk 152 or Mk 141

-Head Mk 10: Base Fuze Mk 146

-Head Mk 10-1: Base Fuze Mk 161 Mod 0

General: The 7.2-inch D.R., a modification of the 7.2-inch H.E., was used for demolition of anti-tank obstacles.  The 7.2-inch D.R. was projected from a multiple-rail armored launcher mounted on the turret of the Tank M4.  It was fired at point-blank range and proved effective against concrete obstacles at ranges of 100 to 150 feet.

 

Description: The rocket has a thin steel head to give the maximum blast effect.  The propellant is the single unperforated cruciform Grain Mk 10.  The body can be fitted with any one of a number of rocket motors to give velocities from 175 to 400 feet per second.  The mean lateral deviation is 10 mils from a 90-inch launcher.

The Base Fuzes Mk 146 and Mk 161 Mod 0 are armed during flight by the pressure of the gas evolved from the burning propellant acting on the diaphragm.  The Head Mk 10 Mod 1 is the Head Mk 10, slightly altered to accommodate the new motor adapter of the Base Fuze Mk 161 Mod 0.


Remarks: The Army designates the Head Mk 10 or Mk 10 Mod 1 as the T37.

A smoke-filled round used by the Army is the same size, and has the designation of T38.  It is nose-fuzed with either the Fuze Mk 152 or the Fuze Mk 141.

The Head Mk 5 may take either the Booster Mk 1 or the Booster Mk 2; the Head Mk 10, only the Booster Mk 1.

The Heads Mk 5 are loaded with TNT; the Heads Mk 10 may also take a TNT load.

7.2-inch C.W.R.N. and M25, M27, and T24

(Motor Mk 5 and Head Mk 7)

Overall length: 48.1 inches

Head width: 7.2 inches

Head length: 18.75 inches

Motor length: 29 inches

Propellant (ballistite): Grain Mk 11

Filler: Any chemical filler with specific gravity over 1.2

Filler (F.S.): 19.7 pounds

Total weight: 53.2 pounds

Range: 3,500 yards

Fuzes: Nose Mk 147 or Mk 147 Mod 1

General: This rocket is fired from a 24-rail demountable, variable-elevation launcher carried in a 2 and 1/2 ton truck.  The salvo is fired in 2.5 seconds, and the launcher can be reloaded in 1.5 minutes.

These rockets of Navy design are under production by the Army.  The only essential difference between the rockets as used by the Army and the Navy is in the propellant.


Head: The container is a bulb-shaped steel tube open at both end.  The adapter fits inside the flange on the forward end of the container and is brazed thereto.  The wide forward end of the adapter is internally threaded to seat the fuze.  The burster tube, made of steel, fits inside the adapter and extends downward into the container.  The tube and adapter are held together by a press fit and sealed with white-lead paste.  The rear end of the tube is closed.


Motor: The motor is a steel tube, with the forward end externally threaded to screw-into the connector of the head.  The nozzle is slipped down through the open end of the motor body, and the end is welded to the inner edge of the motor-body rim.

Tail: The tail assembly has four tail vanes spot-welded in pairs to the motor tube and spot-welded to the rear shroud.  The forward shroud is riveted to the vanes but insulated from them.  Four large fins are welded to the motor tube, pass over the forward shroud, and are welded to the rear shroud.  The lead wires are connected to the two shrouds which serve as contacts.


Propellant: As produced for the Navy, the propellant consists of a single grain of solvent-less extruded ballistite with an outer diameter of 2.5 inches and an inner diameter of 1 inch.  This is the Grain Mk 11.

In the Army Chemical Rocket M25, the propellant consists of four sticks of ballistite, with a one-inch axial hole, placed end to end with separating washers between the sticks.  The sticks are three-ridged, and each has eight sets of holes radially through it.  The overall length of the sticks is 20.5 inches.


Remarks: The Army Rocket M27 is structurally the same as the Navy rocket, but is filled with C/K gas.  Its total weight is 51.8 pounds.

A head similar tot he Mk 7 but loaded with 22 pounds of TNT and equipped with a booster instead of a burster tube is known as the Mk 9.  It is a demolition head, using the Fuze Mk 137 and the 3.25-inch Motor Mk 5.  This combination may be used to lay down a barrage from the same launchers as the C.W.R.N.

When the Head Mk 9 is fuzed with the Fuze Mk 147, it is known as the Round T24.  Its total weight is 51.8 pounds.






11.75-inch A.R. "Tiny Tim"

Overall length: 123 inches

Total weight: 1,253 pounds

Head length: 47 inches

Head weight: 600 pounds

Motor length: 82.4 inches

TNT filling: 152.5 pounds

Fuzes:

-Mk 1 Mod 0: Mk 157 Mk 1

-Mk 1 Mod 1: Mk 157 Mod 2

-Mk 2 Mod 0: Mk 157 Mod 2, Mk 163 Mod 0, Mk 162 Mod 0

Heads: The Mk 1 Mod 0 consists of a standard 500 pound S.A.P. Bomb AN-M58A1 modified for this particular use.  The changes include the removal of the suspension lugs, an increase in the number of threads securing the base plate, the use of a new base plug to take the Fuze Mk 157 Mod 1, and the use of an adapter ring welded around the after end as a means for attaching the rocket motor.  The motor gases are sealed from the high explosive in the body by coating the threads of the base plate with a luting compound, and also by a gasket under the fuze body flange.

The Mk 1 Mod 1 is similar to the Mk 1 Mod 0, except that a projectile-type gas seal is added around the head of the Fuze Mk 157 Mod 2.

The Mk 2 Mod 0 was developed from the Mk 1 Mod 1.  This head differs in that it has a solid-nosed "Common" head and a base plate modified to take three Base Fuzes Mk 157 Mod 2.  The projectile-type gas seal is used around all fuzes and also between the base plate and the forged steel body.  The Fuze Mk 157 Mod 2 is used with one Auxiliary Booster Mk 1 Mod 09, or the Fuze Mk 163 Mod 0 with one Auxiliary Booster Mk 19 Mod 0.

The Head Mk 3 Mod 1 was issued for practice to simulate the Head Mk 2 Mod 0.

The Head Mk 4 Mod 0 is slightly lighter and shorter than previous heads.  The head weight is 578 pounds, including 152 pounds of TNT.  The head length is 46 inches.  Three Fuzes Mk 153 Mod 0 or Mk 162 Mod 0 are used in the base.  The penetrative characteristics of this head are the same as those of rpesent types, but slightly better overall performance may be expected, because of the small increase in velocity resulting from reduction in total weight.

The Practice Head Mk 5 dummies the Mk 4.  It is 44.75 inches long and weighs 569 pounds.  It has a cavity for a smoke puff.

The heads are shipped loaded and fuzed.  A cuff protects the threads on the adapter ring and the fuze during shipment.


Motors: The Mk 1 Mod 0 consists of a steel tube, the after end of which is threaded to receive a plate having twenty-five nozzles.  The motor tube contains four propellant grains of solvent-less extruded ballistite of cruciform cross-section, weighing 147 pounds.  The grains are shielded from each other by an X-shaped partition which extends longitudinally for almost the full length of the motor tube.  The grains and the partition are supported by the grid and are strapped together by aluminum bands.

In normal operation, the gases from the burning powder do not pass through the central nozzle, which is closed by a copper blowout disc.  Only when the pressure in the motor exceeds approximately 22,500 pounds per square inch is this disc expelled, bringing the central nozzle into operation.  The use of a blowout disc allows the rocket motor to perform satisfactorily over a greater temperature range.  It has one disadvantage, however, in that at motor temperatures of about 100 degrees Fahrenheit, where the normal operating pressure is just enough to shear the disc, it is impossible to predict whether it will blow out or not.  If it does, the burning time is lengthened and the gravity drop is increased, so that the rocket may miss the target.

Four black-powder charges of about 0.5 pounds each, contained in plastic cases at the front ends of the grains, provide the ignition for the propellant.  They are set off by two small electric squibs in each case, which are connected to receptacles in the nozzle plate.  The burning of the propellant is markedly affected by its moisture content.   Consequently, the motors are sealed at both ends.  Each of the 24 peripheral nozzles is sealed with a thing steel cup.  The front end is sealed with a thin steel disc having in its center a small blowout window.  This window is blown out by the motor pressure, allowing the propellant gases free access to the base fuze.  These closures should not be removed.

The Igniter Mk 19 Mod 0 has recently been developed for use in 11.75-inch A.R. motors.  Known as a tin-plate case igniter, it consists of a single metal case 3.38 inches in diameter and 1.8 inches deep, with a wall thickness of 0.01 inches.  Four clips are soldered to the base of the case, for attachment to the motor charge support.  The case contains 230 grams of F.F.F.G. black powder.  Contained in the case are two electric squibs connected in parallel to the igniter lead wires.

Motors must never be fired above the rated temperature stenciled on the motor, because they are likely to burst.   Below the lower rated temperature, occasional ignition failures and interrupted burning may be experienced.

The Motor Mk 1 Mod 1 is identical to the Mk 1 Mod 0, except that the motor tube is of higher tensile strength and the pigtail connection has been replaced by two receptacles built into the base plate.

The Mk 1 Mod 2 is a design in which the dead space between the forward motor closure and the base of the rocket head has been eliminated.  This motor is similar in other respects to the Mk 1 Mod 0, except that the overall length has been reduced to 75.75 inches by two receptacles built into the base plate.

The Motor Mk 1 Mod 3 is the Bureau of Ordnance production of the Mk 1 Mod 2.

The Motor Mk 2 Mod 0 weighs 600 pounds and is 72.04 inches in length.  Length and weight reduction have been accomplished by improvements in design detail. so that the total amount of propellant in the motor has not been changed.  Because of design and construction changes, the Motor Mk 2 Mod 0 may be used only with the Head Mk 4 Mod 0.

Next Time: Aircraft Pyrotechnics (Part 1)

American Projectiles and Explosives - Navy Rockets (Part 3)

American Projectiles and Explosives

Navy Rockets






4.5-inch B.R.

(With Head Mk 3)

Overall length: 30 inches

Weight: 28.7 pounds

Head length: 18 inches

Head weight: 19.9 pounds

Wall thickness: 0.25 inches

Motor length: 15.5 inches

Motor diameter: 2.25 inches

Range: 1,000-1,100 yards

Weight of TNT charge: 6.5 pounds

Fuze: Mk 137 or Mk 145

General: The 4.5-inch Barrage Rocket is a light demolition rocket intended for launching from landing boats, from amphibious trucks, or from portable launchers of one or more rails.


Head: The head and motor are coupled by means of a threaded adapter, and the fuze screws into the nose of the head.  The head is cylindrical, the forward and hemispherical and the read end reduced.  About 6.5 pounds of high explosive can be loaded through a 2 and 3/4 inch hole in the rear, which is sealed later with a motor adapter.  The fuze liner, in the nose of the head, contains a booster charge of granular TNT.

Tail Assembly: Two circular shrouds, the same diameter as the body, are attached to supporting fins at the rear of the motor.  Two wires brought out through the powder grain and the nozzle connect to the two shrouds.  The forward shroud is insulated from the rest of the rocket to prevent a short-circuit to the after grounded shroud.

Propellant: The propellant consists of a single cylindrical grain of ballistite 11 inches long, with a 1.7 inch outer diameter.

5-inch A.R. with 5-inch motor

Overall length: 69 inches

Weight: 140 pounds

Head length: 20.3 inches

Head diameter: 5 inches

Head weight: 52 pounds

Motor length: 51.4 inches

Motor diameter: 5 inches

Velocity: 1,350 feet/sec

Fuzes: Mk 5 Mod 0 and Mk 6 Mod 0

-Nose Fuze Mk 148

-Nose Fuze Mk 149

-Base Fuze Mk 157 Mod 0

-Base Fuze Mk 159 Mod 0

Mk 6 Mod 1

-Base Fuze Mk 159 Mod 1

-Base Fuze Mk 164 Mod 0

Head: The Head Mk 6 Mod 0 is filled with TNT and is equipped with a base fuze and a nose plug.  When thus used, the head will have the penetration and fragmentation characteristics at comparable velocities of the 5"/38 AA Common projectile, of which it is a modified design.  All 5-inch Rocket Heads Mk 6 Mods 0 and 1 are shipped with a base fuze installed and staked in place.  No attempt shall be made to remove the base fuze from the head prior to the firing.  A metal cup-shaped thread protector covers the external threads on the base of the head and on the base fuze.

The Mk 6 Mod 1 is similar to the Mk 6 Mod 0, with a gas seal added to the bomb-fuze seat.  The 5-inch Body Mk 5 Mod 0 is the initial California Institute of Technology production, which was adopted by Bureau of Ordnance as the Mk 6 Mod 0.  The two bodies are identical.

The 5-inch Aircraft Common Mk 2 Mod 1 is a new head designed to achieve greater penetration.  This penetration is expected to be two to three inches of homogeneous armor plate at launching speeds of 1,500 feet per second.  The head has a total weight of 48.1 pounds, is 14 inches long, and contains a filler of 2.66 pounds of Explosive "D".  The nose is heavy and solid.  A base fuze (the Mk 166 Mod 0) will be shipped installed.  This head will fit any of the 5-inch motors.

The Head Mk 2 Mod 2 has no adapter and has Acme thread; otherwise it is the same.

Motor: The 5-inch Motor Mk 2 Mod 0 consists of a seamless steel tube with internal threads on both ends.  Into the rear end is screwed the nozzle plate having eight nozzles arranged in a circle, and a central blow-out nozzle.  The central nozzle is closed by a disc of 0.024-inch thick copper, insulated against the heat of the motor by asbestos and hard fiber plugs.  The thickness of the disc is such that it shears and blows out at a pressure of approximately 2,400 pounds per square inch, which is the normal maximum motor pressure when the propellant grain is at a temperature of 100 degrees Fahrenheit.  If the pressure rises above this, the disc and plug are ejected; this increases the usable temperature range of the rocket by about 40 degrees Fahrenheit.

Seven of the eight nozzles are sealed individually by a light steel cup and sealing compound.  The eight nozzle accommodates the electric connector cable, which is crimped into the steel nozzle closure.  In shipment, a dome-shaped steel shipping cap fits into the sleeve of the fin assembly, acting as an auxiliary seal and at the same time serving to enclose and protect the electrical pigtail in shipment.

Lugs for attaching the fins are mounted on the nozzle end of the motor.  The fins are shipped with the motor and are attached when the round is assembled.  The fins are held in place by spring-loaded latches within the fin itself.  The fin lugs and rear suspension lugs are welded to the bands of the fin assembly, which is slipped on over the nozzle end of the motor.  The front lug band is strapped to the motor.  The motor is shipped with lug attachments on the motor tube for use with Aircraft Launcher Mk 5 Mod 1.  An extra rail-type lug is provided in the shipping box to adapt the rocket for use on the Aircraft Launcher Mk 4.

The front end of the motor is sealed by a steel diaphragm equipped with a blow-out disc in the center to allow easy passage of the motor gases to the pressure-arming fuze in the base of the body.  In shipment, a cylindrical metal thread protector extends into the motor the same depth as the body and seats on a felt rim glued to the diaphragm seal.

The propellant is a grain of cruciform ballistite weighing 24 pounds.  The grain is inhibited on the outer web surface and is supported by a spacer and a steel grid at the nozzle end.  The propellant is ignited by a metal case igniter containing 35 grams of black powder.

The 5-inch Motor Mk 2 Mod 1 was never produced.  The Mk 2 Mod 2 differs in that the tail fins are welded to a sleeve which slips over the base of the tube and is clamped in place.  The fin assembly is complete and separate from the motor.  The rear suspension lug for use with the Launcher Mk 5 Mod 1 is on an independent band.  The Mk2  Mod 3, which will supersede the Mods 0 and 2, is similar to the Mod 2, except that the nozzle ring is of slightly different construction.

The 5-inch Rocket Motor Mk 1 Mod, California Institute of Technology production, is the prototype of the Mk 2 Mod 0, Bureau of Ordnance issue.  The two motors vary only in that the suspension lugs on the former are welded directly to the rocket motor.

5-inch S.S.S.R.

General: The General Purpose and Common rounds are particularly adapted for repelling PT-boat attacks at ranges less than 11,000 yards.  The High-Capacity rockets are suitable for barrages at 1,250 to 5,000 yards.  These rockets must be used in the specially designed Launchers Mk 50 Mods 0 and 1 and Mk 51 Mods 0 and 1; and in Launcher Assemblies Mk 101 Mod 0 or Mk 102 Mod 0.



Heads

5-inch Head Mk 7 - General Purpose: This head is threaded externally at the after end to accommodate the motor.  It is threaded internally at the forward end to accommodate the fuze adapter for Rocket Fuze Mk 100 and Mods.  Two spanner holes are located in the after end of the head spaced 180 degrees apart to facilitate assembly.  The fuze adapter is internally threaded for Auxiliary Detonator Fuze Mk 44 Mod 2.  The Nose Fuze Mk 100, all Mods, is screwed in over the Auxiliary Detonating Fuzes.  (The fuze adapter and an Auxiliary Detonator Mk 44 Mod 2 are shipped installed in the head.)


5-inch Head Mk 8 and Mods - Common: The head is internally threaded at the after end to take Base Fuze Mk 31.  It has two spanner holes 180 degrees apart to facilitate assembly operations.


5-inch Head Mk 10 and Mods - High Capacity: The nose of this head is internally threaded to fit Nose Fuze Mk 30 Mod 3 and a fuze adapter.  It has two spanner holes 180 degrees apart near the base end to facilitate assembly operations.  The fuze adapter is internally threaded to hold Auxiliary Detonator Mk 44 Mod 1, and the Nose Fuze Mk 30 Mod 3 fits over the auxiliary detonator.


5-inch Head Mk 12 and Mods - High Capacity: The 5-inch Head Mk 12 and Mods is 3.125 inches longer than the 5" Mk 10 head used in the 5,000 yard round.  It carries 2/8 pounds more TNT than the Head Mk 10.


5-inch Head Mk 13 and Mods - High Capacity: The 5-inch Head Mk 13 and Mods is 4.78 inches longer than the 5" Head Mk 10.  It also carries about four pounds more TNT.




Motors

5-inch Motor Mk 3 and Mods: The motor tube is a seamless steel tube with internal threads at both ends.  It is machined with a bourrelet ring at each end.  The front closure is a steel disc pressed in position near the front end of the motor tube.  It seals the front end from moisture, dirt, etc., and retains the igniter and propellant grain in place.  A thin felt pad cushions any contact between the front closure and the igniter.  The Igniter Mk 17 Mod 0 consists of a flat tin case containing 35 grams of black powder and an electric squib.  A felt disc one inch thick protects the grain from accidental shock.  It has an eccentrically placed hole which houses and forms a snug fit for the igniter case.

The propellant is an inhibited, cruciform grain weighing approximately ten pounds.  The nozzle plate assembly consists of eight nozzles and a grid mounted on a nozzle plate.  The cylindrical T-shaped steel grid is pressed into place and peened in position in a center hole in the nozzle plate.  It acts as a spacer between the grain and the nozzle plate, creating a chamber which equalizes the pressure to all nozzles during burning.  The nozzles are press fitted into the plate and are canted 12 degrees to give a clockwise rotation.  The nozzle-plate ring assembly consists of a nozzle-plate ring and the insulated contact ring.  The contact ring is a steel band around the nozzle-plate ring and is insulated from it.  The plate ring and contact ring are the two terminals of the ignited electrical circuit.  The rings are short circuited by a band.  The short-circuiting band must be removed when preparing the rocket for firing.  The rear closure is a thin aluminum cup cemented in place in the after end of the motor, and blows out after the motor pressure builds up.


5-inch Motor Mk 4 and Mods: The 5-inch Rocket Motor Mk 4 is similar to the Mk 3 discussed above, except that the motor tube is seven inches shorter than the Motor Mk 3.  The Igniter Mk 18 with shorter leads is used.  Propellant Grain Mk 22 Mod 0, shorter and weighing approximately 5.5 pounds, is used.  The nozzle in the nozzle-plate assembly has a smaller throat diameter.


5-inch Motor Mk 5 Mod 1: The Mk 5 Mod 1 is similar to the Mk 4, except that it is 3.125 inches shorter and the nozzle plate has four instead of eight nozzles.  This shorter motor gives a range of 2,500 yards and a maximum velocity of 475 feet per second, which is suitable for barrage purposes.


5-inch Motor Mk 6 Mod 0: The Mk 6 Mod 0 is also similar to the Mk 4 and Mods, except that it is 4.78 inches shorter and the nozzle plate has only four nozzles.  The cant of these nozzles has been increased to insure stable flight of the round at slower velocities.  This shorter motor gives a range of 1,250 yards and a maximum velocity of 340 feet per second, which is suitable for barrage purposes.

Next Time: Navy Rockets (Part 4)

American Projectiles and Explosives - Navy Rockets (Part 2)

American Projectiles and Explosives

Navy Rockets






3.5-inch Window

Overall length: 45.1 inches (approx.)

Weight: 32 pounds

Head length: 23.2 inches

Head weight: 14.25 pounds (loaded)

Motor length: 23 inches

Motor diameter: 3.25 inches

Width of tail fins: 9.2 inches

Length of tail fins: 8 inches

Fuze: Base Fuze Mk 134

General: The window rocket is designed to be fire from Naval vessels equipped with a modification of the present shipboard launcher.  The round carries a payload of paper-coated metal foil strips which are scattered in the air by a delayed-action charge.  The payload is ejected at an altitude of 1,200 feet and range of 2,000 yards at 40 degrees of elevation.


Description: The window rocket consists of a 3.5-inch Rocket Head Mk 10, Mk 14 Mod 0, or Mk 15 Mod 0 and a 3.25-inch Rocket Motor Mk 12 Mod 0, Mk 14 Mod 0, or Mk 14 Mod 1.  The motor uses the propellent grain Mk 7 Mod 1, weighing 2.8 pounds.


The rocket head contains a 3.5-inch rocket-head load - Mk 2, Mk 3, Mk 4, Mk 5, or Mk 8 - which is housed in a split steel ejection liner.  It has a closure adapter on the after end, an obturator cup for sealing the front end, and a solid wood ogive cap retained by three aluminum rivets in the Mk 10, hollow-steel friction fit in the Mk 14 and Mk 15.  The closure adapter, which is welded to the after end, carries a copper diaphragm plate with a firing pin, and also serves as a chamber for the Cal. 32 blank cartridge which ignites the fuze.  The Fuze Mk 134 consists of a plastic case containing a length of Ensign Bickford fuze and a 20-gram ejector charge of black powder.

All strips are 3/16 inches wide and 0.008 inches thick except the Mk 9, which are 1/2 inch wide.



Operation: When the rocket is fired, gas pressure blows out the forward closure disc of the motor and exerts force on the diaphragm plate in the base of the motor adapter.  The diaphragm collapses, and the firing pin is forced into the primer, firing the blank cartridge. The flash from the cartridge ignites the fuze, which burns for 15 seconds and then ignites the black powder ejection charge.  The firing of the ejector charge forces off the ogive cap and pushes the load forward out of the head.  The strips are then dispersed.


Remarks: The Motors Mk 12 Mod 0 and Mk 14 Mod 0 carry adjustable lug bands; the lugs are welded to the Motor Mk 14 Mod 1.  The Mk 14 Mod 0 and Mk 14 Mod 1 have a metal base cap during shipping, to protect the electrical connector.

The head Mk 15 Mod 0 is one inch longer than the Head Mk 14 Mod 0

3.5-inch Flare

Overall length: 47 inches (approx.)

Weight: 33.5 pounds

Head length: 23 inches

Head weight: 16.5 pound

Motor length: 24.5 inches

Motor diameter: 3.25 inches

Fuze (Head Mk 14): Base Fuze Mk 134

Fuze (Head Mk 15): Base Fuze Mk 128

General: The 3.5-inch rocket flare was developed for use from surface ships, particularly motor torpedo boats.  The illuminant candle produces an average of 800,000 candle power for approximately twenty-nine seconds.  The rocket motor carries the flare out 1,800 yards before ignition.

The flare consists of the following major components: 3.25-inch Motor Mk 12 Mod 0, Mk 14 Mod 0, or Mk 14 Mod 1; 3.5-inch Head Mk 10 Mod 0, Mk 14 Mod 0, or Mk 15 Mod 0; and Body Load (Flare) Mk 7 Mod 0.


Head: All the heads are interchangeable and differ only in minor details.  The 3.5-inch Head Mk 10 Mod 0 has a wooden nose piece held in place by three shear pins, while the Mk 14 Mod 0 and Mk 15 Mod 0 have a sheet-metal nose piece press-fitted in place.  The Mk 15 Mod 0 is one inch longer than the other two.

The head consists of a 3.25-inch seamless steel tube which incorporates a 3.5-inch diameter closure adapter welded to the after end.  This closure adapter carries a copper diaphragm plate with a firing pin, and serves as a chamber for the caliber .32 blank cartridge which ignites the fuze.  The balance of the head is taken up by the candle and parachute from the 4-inch illuminating projectile, the composition of the candle slightly changed to increase the candle power in the shorter burning time.

Motors: The three motors are similar and interchangeable.  The principal distinguishing feature of the 3.25-inch Motor Mk 14 Mod 1 is the use of welded-on launcher lugs replacing the lug bands employed on the earlier models.  The motor housing is a 3.25-inch seamless steel tube containing a forward closure disc, Igniter Mk 11 Mod 0, Tubular Ballistite Grain Mk 7 Mod 1 (2.8 pounds), steel grid, welded nozzle, and pigtail.  Four tail fins, three inches by eight inches, are mounted on a sleeve fixed to the after end.  A thread projector on the forward end and shipping cover taped on the after end protect the motor in shipment.  The 3.25-inch Motor Mk 12 Mod 0 does not have a shipping cover on the after end.



3.5-inch and 5-inch A.R. with 3.25-inch Motors

General: The 3.5-inch rockets were designed to be used against smaller targets, such as submarines and tanks.  For larger targets, the 5-inch rocket was developed from the 5-inch anti-aircraft shell.  The 3.5-inch Solid Head Mk 8 and the 3.5-inch F.S. and P.W.P. Smoke-filled Heads Mk 6 are the only ones now being issued.  The 3.5-inch H.E. heads were replaced by the 5-inch heads.  The former were never issued, because of the small load of TNT carried, as compared to the 5-inch heads.


Heads


3.5-inch Mks 1 and 2: The head is of solid steel and contains no high explosive or fuze.  The shape of the round gives a relatively long underwater travel at shallow depth-of-entry angles (about 20 degrees), and it is used as a semi-armor-piercing projectile against submarines or tanks.  The Mk 1 was the California Institute of Technology production which was adopted by Bureau of Ordnance and designated the Mk 2.


3.5-inch Mks 3 and 5: The head is filled with TNT and fitted with an adapter in the nose to take the Fuze Mk 149.  With a second adapter, the diameter is reduced to 1.5 inches to take the Fuze Mk 148.  These rounds were not issued and were replaced by the 5-inch heads, which contain a greater load of high explosive.


3.5-inch Mk 4: The head has a semi-armor-piercing nose and is filled with TNT.  This round was not issued, because of the small load of high explosive, and was replaced by the 5-inch heads.

 

3.5-inch Mks 6 and 9: The head is filled with F.S. or P.W.P. smoke.  The Mk 9, the initial California Institute of Technology production, was not issued.  The Bureau of Ordnance, in adopting this head, increased the length 1-1/2 inches and issued the round as the Mk 6.

3.5-inch Mk 8: The head is of solid steel and contains no high explosive or fuze.  The round was developed to give better underwater travel and replaces the 3.5-inch Head Mk 2.


5-inch Mk 1 Mod 0: The head is filled with TNT and weighs 46.5 pounds when fitted with a Fuze Mk 143.  The same adapter rings are used as on the 3.5-inch Head Mk 5.  The head is issued with a nose plug.  The nose fuze must always be assembled in the head before firing.  Fire with the fuze on "safe" if delay is desired.  The head is shipped with the base fuze sealed in place.  This base fuze must not be removed.


5-inch Mk 1 Mod 1: This head differs from the 5-inch Head Mk 1 Mod 0 only in that the nose is especially cavitated to take the Fuze Mk 172 Mod 0, which is larger than the Mk 149 or other nose fuzes and therefore is not interchangeable with them.




Motors


The 3.25-inch Motor Mk 7 is used with the 3.5- and 5-inch heads described above.  At the forward end of the motor are a black-powder igniter and an electric squib.  Two electric leads extend through the motor and out the after end to a cable and plug connection.  At the after end of the motor, there are a nozzle and a bag of silica gel which acts as a dehydrating agent in keeping moisture from the ballistite grain.  The grain used in the cruciform type with inhibitors, 33 inches long, 2.75 inches in diameter, and weighing 8.5 pounds.

The tail consists of four sheet-metal fins set 90 degrees apart and welded to a central cylinder.  The tail is slipped over the after end of the motor and is secured by a tail locking ring, which screws on.


Remarks: The 3.5-inch (H.E. and F.S.) have a maximum velocity of 1,200 feet/sec exclusive of plane speed, as compared to 800 feet/sec for the 5-inch H.E.

The 3.5-inch Heads Mk 11, incendiary, and Mk 12, gas, were never loaded.

Next Time: Navy Rockets (Part 3)

American Projectiles and Explosives - Rocket Bodies, and Navy Rockets (Part 1)

American Projectiles and Explosives

Rocket Bodies Introduction

General

 The propelling unit of the rocket is called the motor and contains the propelling charge.  The motor is attached to the head, which contains the payload and the initiating device.  The motor is closed on the forward end and partially opened at the after end.  The propellant is a relatively slow-burning double-base smokeless powder called ballistite.

As the ballistite is burned, hot gases are generated which expand and exert pressure against the confines of the motor tube.  Since the hot gases exert an equal pressure in all directions, the pressures against the side walls counter-balance each other; however, the pressure against the forward closed end of the tube is not counteracted by pressure against the after end since that end is partially open.  The resultant force, then, is a thrust against the closed forward end of the motor, and the rocket is propelled in that direction.  In order that the pressure of the gases will not be expended too rapidly, and that the propellant can be retained in flight, the after end of the motor tube is partially closed by the nozzle attachment, which is built into the inside of the tube.  This nozzle restricts the ejection of the hot gases and also, by means of its rear taper, furnishes a canted surface against which the rapidly expanding emitted gases may act to increase the forward thrust of the rocket.

The ballistite propellant is ignited by a black-powder charge, the initiating device for which is an electric squib with a small bridge wire of high resistance which, when heated by an electrical current, ignites a violent match composition.  The black powder charge sends a flash over the entire surface of the ballistite to the ignition point.  Upon ignition, the ballistite burns evenly and relatively slowly; this type of burning is necessary to prevent sudden and excessive pressures being exerted against the thin walls of the motor tube.  Rocket motors operate at much lower pressures than guns, and correspondingly longer times are required for the complete combustion of the rocket propellant.  Burning times of American rockets range from about 0.15 seconds to as much as 1.5 seconds, depending on the web thickness of the grain and the temperature of the propellant; and burning distances range from a few feet to several hundred feet at high velocities; hence, most of the burning of the rocket propellant occurs after the projectile has left the launcher.

The early productions of rockets were of the fin-stabilized type because of their use by the British and because of the inherent simplicity associated with fin stabilization.  Rockets cannot be launched with that degree of accuracy characteristic of gun projectiles.  This is a result of many factors, such as the effect of temperature on the burning rate of the propellant, difficulties in controlling to a fine degree the pressures exerted by the expanding gases inside the motor tube, the effect of the expansion of emitted gases against the rear taper of the nozzle, etc.  The mean deviation in deflection for most standard land- or shipboard-launched fin-stabilized rockets is 20 to 40 mils, while fin-stabilized rockets launched from aircraft have a mean deviation of about 5 to 10 mils.  The increased accuracy of aircraft-launched rockets is attributed to the immediate stabilizing effects given to the fins during the initial stages of flight by the rapid travel of the plane through the air.  Fins on rockets exert an appreciable restoring force in flight only at a high velocity, and thus a greater degree of accuracy is achieved if rockets are launched from aircraft or if the acceleration occurs to a large extent on the launcher.

A later development, the spin-stabilized rocket, is now in service use.  Stabilization of this rocket depends on the rotation of the round.  Although the accuracy of spin-stabilized rockets is not comparable to that of gun projectiles, they are generally more accurate than fin-stabilized rockets at short ranges.  The use of spin-stabilized rockets will be particularly advantageous to ground and amphibious forces, inasmuch as the rocket is shorter and the launching gear is more compact, facts which facilitate the loading and stowage problems.

As against their disadvantages, rockets have many advantages over gun-propelled projectiles.  The most important is the absence of recoil against the launcher.  Since there is no recoil action on the launcher, rockets may be launched from small trucks, amphibious ships, and aircraft which could not withstand the recoil forces exerted by equivalent projectiles fired from guns.  Other advantages of rockets are cheapness, simplicity, and portability of the launchers as compared to guns.

Components



Head: This is the part which is functionally similar to a projectile and which contains the payload and the initiating device.  This payload may be solid shot, high explosive, chemical, incendiary, window, flare, or a special load.


Motor Tube: This contains the propelling charge and the igniter.  It is a combustion chamber in which the propellant is burned to provide the motive power for the rocket.  It generally threads to the rocket head and is usually shipped separate from the head and fuze.  The diameter of the motor is generally less than the diameter of the body with which it is used.


Grid or Trap assembly: The Navy refers to the assembly which supports the powder grain as the grid.  This grid supports the grain in such a position that sufficient clearance is allowed between the grain and the motor tube to allow the gas to flow from the propellant to the nozzle.  The Army uses a trap assembly, which is somewhat more complicated than the Navy grid.  The trap assembly consists of spacing discs and wires running between them, on which the sticks of ballistite are supported.  Such an assembly is necessary where numerous small grains are used.


Nozzle: The number of nozzles varies with the type of motor and method of stabilization.  The nozzle has several functions.  It directs the gas jet in the desired direction and provides for expansion of the hot gas in the exit cone, thus giving additional thrust (about 33%) over the obtainable from a simple orifice.  In spin-stabilized rockets, it imparts a clockwise rotation tot he rocket when launched.


Fins: During burning, the action of the air against the fins gives a restoring moment against side forces at the nozzle, thus improving the accuracy of fire.  When there is a tail shroud, it supports the rear end of the rocket in the launcher and may also provide electrical contacts for firing.


Propellant and igniter: The igniter contains loosely packed black powder and an electric squib with a high-resistance bridge running through a match composition.  The propellant is a double-base smokeless powder called ballistite, which burns slowly and uniformly.  Production of ballistite differs somewhat for the Army and the Navy, the Army preferring the solvent extrusion process and the Navy specifying the solventless extrusion process.  The solvent extrusion process is impractical for grains having a web of more than 1-1/4 inches.

Grain shapes also vary.  Army rockets generally have several small cylindrical grains of ballistite, with an axial hole to increase the burning surface and uniformity of burning.  The Navy rockets use either a single solid cruciform grain without perforation or a single cylindrical grain with an axial hole and radial perforations.  The latter, used in Navy ground- or shipboard-mounted rockets, is characterized by three ridges 120 degrees removed and running longitudinally along the grain.  Inhibitors are not used on this type.  The cruciform grain, in Navy aircraft rockets, is a symmetrical cross with rounded ends.  If all the exterior surface of this grain were permitted to burn, there would be a gradual decrease of area, and a regressive rate in burning.  Hence, a number of slower burning cellulose acetate strips are bonded to parts of the area exposed on the outer curved ends of the arms, to give desired burning characteristics.


Storage:  To decrease hazards in handling, rocket bodies and motors are generally shipped and stored separately.  Motors with large grains are kept in a non-propulsive state until final assembly is necessary.  The seals at both ends of the motors are light and easily displaced by pressure developed inside the tube.  Should the igniter and grain igniter, the closures would fail quickly, relieving the pressure without more than a slight movement of the motor.

It is necessary that loaded motors be kept at moderate temperatures as much as possible.  Event hough spontaneous ignition should not take place, the powder should not be stored where temperatures exceed 100 degrees Fahrenheit, because such conditions tend markedly to decrease the stable life of the propellant.  Because of the electric squib, rocket motors should not be stored near radio apparatus or antenna leads.

Although there is very little possibility of a motor firing as a result of falling or rough handling, such treatment is likely to cause malfunctioning of the rounds.  Ammunition should be kept in packing containers or ready boxes and should not be handled in a loose condition unless necessary.

Practice Rockets

Practice rockets are loaded with plaster of paris or other inert substances to simulate the explosive loads in service rounds.  These rockets also have dummy fuzes.




Safe Temperatures

The burning rate of propellent powders changes with temperature and pressure - the higher temperatures and pressures causing more rapid burning.  If rockets are fired at temperatures higher than those for which they are designed, the pressure may build up faster than the nozzle can release it, perhaps bursting the round.  At temperatures below the safety limit, there will be back blasts of flame with burning fragments of powder.

Retro Rocket

These were rockets designed to be fired aft from a fast moving ship or plane - the movement aft to compensate exactly for the movement forward of the launching vehicle, thus leaving gravity as the only effective force on the rocket.

2.25-inch A.R. Practice

General: The 2.25-inch sub-caliber rocket rocket for aircraft was developed for training purposes.  Initially, two types were designed to approximate the trajectory of the 3.5-inch and 5-inch rockets; however, only the Motor Mk 11 and the Head Mk 3 Mod 2 will be used in future training.

The Mk 1, a California Institute of Technology production, was issued until adopted and issued by Bureau of Ordnance as the Mk 3 Mod 2.  The Mk 2, a California Institute of Technology production, was designed as a slow sub-caliber rocket.  The complete assembly for the latter is no longer available.

The 2.25-inch Motors Mk 10 and Mk 11 are similar to each other, as are the 2.25-inch Motors Mk 12 and Mk 13.  The Motors Mk 10 and Mk 11 differ from the Mk 12 and Mk 13 in that the diameter of the nozzle on the latter is smaller and the weight of the propellant of the Mk 10 and the Mk 11 is 1.75 pounds, as compared to the weight of 1.12 pounds in the Mk 12 and Mk 13.

The external dimensions of the rockets are the same.  For recognition purposes, the 2.25-inch motors Mk 10 and Mk 11 are painted white with black fins, while the Motors Mk 12 and Mk 13 are grey with black fins.


Motor Mk 11 and Head Mk 3 Mod 2: Overall length of the rocket is 29 inches.  Two button-type lugs are provided ont he motor tube, spaced approximately 19 inches apart.  Four fins are welded to the after end of the motor tube.  The propellant is a cylindrical grain of ballistite weighing approximately 1-3/4 pounds.

3.25-inch Targets

General: As a target for anti-aircraft gunners, the rocket is projected with speeds approximating those of an aircraft.  It consists of a rocket propulsive unit to which are attached large stabilizing fins, for maximum visibility.  They all consist of a simple rocket motor with three large fins prepared from wooden frames and light-weight fiber board.  The fins are 120 degrees apart, each attached by two lugs.

The 3.25-inch Rocket Targets Mk 1 and Mk 2 consist of a motor 36 inches long, to which fins 18 inches by 34 inches are attached.  An electrical connection is made by a standard 110-volt plug.  The 3.25-inch Target Rocket Mk 1 is standardized at 425 mph and the Mk 2 at 300 mph.  On some models, a screamer is put over the nose end.

The Mks 3 and 4 differ from the Mks 1 and 2 in that the motor is heavier and the fins are held on by threaded studs instead of lugs.  The ballistics are similar; Mk 3 is like Mk 1, and Mk 4 is like Mk 2.

Next Time: Navy Rockets (Part 2)