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)