American Projectiles and Explosives - Explosive Bombs - "AN" Series (Part 1)

American Projectiles and Explosives



Explosive Bombs

"AN" Series

Introduction

The creation of the Army-Navy Standardization Board resulted in the standardization of the bombs of these two services into the AN series.  This series was very similar to the M series except for these modifications:

1. A third suspension lug was added at the center of gravity and diametrically opposite the dual suspension lugs, to fit British release devices.

2. The base plate was changed to a male plug to increase the strength on low-angle penetration of targets.

3. The bombs were painted an overall olive-drab with one-inch yellow bands around the nose and base, and a 1/4-inch yellow band around the center of gravity.

The bombs in this series included the following weights: 100, 250, 500, 1,000, and 2,000 pounds.  These bombs are all general purpose high-explosive bombs.  Thought other types of bombs - armor-piercing, semi-armor-piercing, fragmentation, incendiary, depth, etc. - have been subsequently standardized and given AN designations, it is with the AN general purpose bombs and their modifications that this introduction shall be concerned.

AN G.P. Series: The AN series was subsequently replaced by the AN G.P. series to make it possible for these bombs to be used in anti-submarine work as well as for general bombardment.  This modification was incorporated into the 500-, 1,000-, and 2,000-pound bombs only, their new designations becoming AN-M64, AN-M65, and AN-M66, and consisted of a change from the Adapter Booster M102 to the Adapter Booster M115.  With the Adapter Booster M115, it became possible to use either standard Army tails fuzes or the Tail Hydrostatic Fuze AN-Mk 230.  The standard filling of these bombs was 50/50 Amatol until the supply of TNT became ample in 1943, at which time TNT became the standard filler.  At the present time, 25% of the production of these bombs is filled with Composition "B".

AN G.P. A1 Series: The A1 modification consists of two steel pins in the base plate which lock the base plate to the main filling, thus preventing removal of the base plate, once the bomb is filled.  In this series the adapter boosters have also been modified to the M102A1 and the M115A1.  This modification consists of a hole through the adapter booster and a groove in the threads of the base plate to receive a locking pin which is shipped with all anti-withdrawal tail fuzes.  Insertion of the pin which is held in by the fuze body prevents withdrawal of the adapter booster.  This series is the current production G.P. bomb series and is used jointly by the Army, Navy, and British forces.

Body Construction: The body construction of American G.P. bombs may be in one, two, or three pieces.  Methods of manufacture include (1) one-piece cast or spun, (2) two-piece cast and welded, or (3) three-piece cast and welded.

The ogival nose tapers to join in the thin parallel side walls, which terminate in a boat-tailed shape at the after end.  The threaded nose opening is closed by the fuze-seat liner, and the threaded base opening is closed by a male plug, the tail fuze pocket being made by the adapter booster.

Suspension: Dual suspension lugs for horizontal suspension are welded directly to the bomb case, being spaced 14 inches apart on bombs up to 2,000 pounds, and 30 inches apart on bombs 2,000 pounds and over.  A single horizontal suspension lug is also welded to the bomb case at the center of gravity and diametrically opposite the dual lugs.  The lugs are eyebolts, shaped from bar steel and formed in the shape of a "U".  "M" series bombs could be carried on single suspension racks by using an additional single-suspension lug welded on a band fitting around the bomb body at the center of gravity.

For suspension in dive-bomb displacement gear, trunnions are provided on a separate band which may be one of two types.  The first type provides the trunnion only; and the second, a more common type, provides a single hoisting lug in addition to the trunnions.  On some of the newer designs of AN bombs of Navy manufacture, the suspension and hoisting fittings are not attached to the bomb case by welding, but are held to the case by threaded bolts fitting into holes tapped and threaded into the body.  For suspension in torpedo slings, the torpedo sling guide key found on Navy bombs can be made on AN bombs by using the base of the single suspension lug with the lug removed by gentle hacksawing.

To hoist bombs into Navy planes, the AN bombs not equipped with hoisting lugs must have a hoisting lug furnished by either an expendable band with single or dual lugs, or by a removable hoisting band.  The removable band is preferred, since it does not affect the terminal velocity of the bomb.  The newest and best of theses bands is the Universal Hoisting Band Mk 8.  For Army planes, bombs are usually hoisted by canvas slings, which also have the advantage of not affecting air trajectory.

Tail fin construction: The tail construction is known as the box-type tail and consists of the following parts: a cast-steel sleeve secured to the body of the bomb by a fin locking nut, and four sheet-steel supported by four sheet-steel struts in the shape of a box.  One fin and one strut are pressed from a single piece of metal, and the four pieces are then welded to the sleeve.  "A" indicates heavier construction for high-altitude bombing.

Color and markings: The standard color scheme employed on these bombs since 11 March 1942 has been olive drab body with yellow bands to indicate the H.E. filler.  The banding system for Amatol and TNT fillers is a one-inch yellow band at the nose, a one-inch yellow band at the tail of the bomb body, and a 1/4-inch dotted band at the center of gravity.  Because Composition "B" is more sensitive and requires more careful handling, it is given an additional marking consisting of a second one-inch yellow band at the nose and at the tail.  On these bands "Comp. B" is stenciled in black paint.  Recent production eliminates the 1/4-inch band, since the center of gravity is located accurately enough by the single suspension lug.

The following standard markings are painted on the bomb body in black paint: type, weight, and name of bomb, type of filling, lot number, place and date of filling, and inspector's initials.

Additional indestructible marking is stamped into the metal of the bomb case on the rear conical surface of the bomb body: type, size, name, maker's initials, lot number, and date. 

(IE: G.P. 500 lb. AN-M64 CSCO Lot 57 4/42)

Explosive filling: The filling of these bombs is accomplished in the following manner.  With the nose-fuze seat liner in place, the bomb is placed on end nose-down and an Auxiliary Booster M104 is positioned behind it.  The M104 is a bakelite tube containing tetryl pellets.  The initial pour of the explosive is sufficient to secure the auxiliary booster when it cools.  Then the remainder of the filling, 50/50 Amatol, TNT, or Composition "B", is added until a depth of approximately six inches remains to be filled.  A second Auxiliary Booster M104 is then inserted in all bombs except the 100-pound, and the tail surround is added to complete the filling.  A wooden former is inserted in the tail-fuze cavity as the filling cools.  After cooling, the former is removed and the appropriate adapter booster is inserted.  The adapter booster consists of the fuze-seat liner with an additional steel cup containing a tetryl pellet.  The Adapter Booster M102 (and M102A1) has an internal thread diameter of 1.5 inches.  The adapter Booster M115 has an internal thread diameter of 2 inches, and an adapter ring for further reduction of the diameter to 1.5 inches when smaller fuzes are used.

Tests conducted by the Army indicated that the presence or absence of Auxiliary Boosters M104 does not alter the effectiveness of the detonation of bombs.  On the basis of these tests, the Army started to eliminate the Auxiliary Booster M104 from Composition "B" loaded 500-pound, 1,000-pound, and 2,000-pound G.P. bombs during the latter part of 1944.  Elimination of Auxiliary Boosters M104 in TNT and Tritonal loaded G.P. and S.A.P. bombs was started in March (TNT) and June (Tritonal) of 1945.  At the present time, all productions of Composition "B", TNT and Tritonal loaded G.P. and S.A.P. bombs, and Composition "B" loaded Frag. bombs, exclude Auxiliary Boosters M104.


The bombs from which the Auxiliary Boosters M104 are now eliminated are as follows:

Tests conducted by the Army have shown that inert nose and tail surrounds improve safety in handling of G.P. and S.A.P. bombs.  On the basis of these tests, the majority of G.P. and S.A.P. bombs loaded at the present time have inert nose and tail surrounds.  This covers Composition "B", TNT, Tritonal, and Picratol filled bombs.  Formerly Composition "B" loaded bombs had TNT surrounds.

The ingredients of the inert surrounds used at present are as follows:

Ester gum, 51%
Castor oil, 10.5%
Kaolin, 34.5%
Wax, Hydrocarbon, 4%


The thickness of these surrounds is as follows:

The thickness of the surrounds is such that most, if not all, of the explosive portion of the adapter booster and that of the nose-fuze booster (surrounded by fuze seat liner) extends into the main filler, with exception of the S.A.P. nose setup.



Anti-Ricochet attachments: To give a more nearly vertical impact to 100-pound, 250-pound, and 500-pound G.P. bombs and to break their rapid descent when dropped from low-flying planes, the Anti-Ricochet Devices M16 and M17 have been developed.  The device consists of a parachute unit, a modified AN-M112A1 series tail fuze (M151) using an anemometer-type arming vane, and a fuze adapter.

Cluster and cluster adapters: Properly, the cluster adapter is merely the containing device or holder.  When the adapter is loaded with bombs, the entire assembly becomes a cluster.  In some cases the cluster adapter may closely resemble a bomb in construction (e.g. M15 and M16), while in others the adapter is nothing more than a banding arrangement (AN-M1A1, AN-M4).

Next Time:"AN" Series (Part 2)

American Projectiles and Explosives - Explosive Bombs - Navy "MK" Series (Part 2)

American Projectiles and Explosives



Explosive Bombs

Navy "MK" Series

650-pound Depth Mk 38 (TNT) and Mk 49 (Torpex) (Obsolete)

Overall length: 58.5 inches
Body length: 36.4 inches
Body diameter: 17.7 inches
Wall thickness: 0.12 inches
Tail length: 29 inches
Tail width: 17.7 inches


Filling: TNT
Weight of filling: 425 pounds
Total weight: 634 pounds
Charge/weight ratio: 67%

or

Filling: Torpex

Weight of filling: 472 pounds
Total weight: 681 pounds
Charge/weight ratio: 69%

Body construction: The body is constructed in three pieces, the flat nose and tail pieces being welded onto the sheet-steel center tube.  The suspension lugs are reinforced with a strip of sheet steel.


Suspension: Horizontal suspension is provided by the usual two suspension lugs, with threaded holes on each side 90 degrees removed to receive the trunnion lugs for suspension from dive bombers.


Color and markings: TNT-loaded bombs have Mark numbers and weight stencilled in yellow; Torpex-loaded bombs have markings in blue.


Tail construction: Four vanes are supported by a circular strut.


Remarks: AN-Mk 219 will not arm under 2,500 feet of altitude if the flat-nose attachment is used.  An Adapter Mk 219 and an additional Auxiliary Booster Mk 1 must be used with this fuze.

Mk 221 arms with difficulty, and should not be used because of delay.

AN-M103 or AN-M103A1 will not arm with the flat-nose attachment, unless special arming vanes are used.

An extender is supplied with each bomb to permit installation of the Hydrostatic Fuze AN-Mk 224 or AN-Mk 234 in the longer athwartships tube.

Because of numerous instances in water crash landings where depth bombs fuzed with the Athwartships Fuze AN-Mk224 or AN-Mk 234 exploded, these two fuzes have been suspended from use.  As a consequence, the Depth Bombs Mk 38 and Mk 49 may be used only if a nose impact fuze is installed.

30-pound Frag. Mk 5 Mods 0-3 (Obsolete)

Overall length: 22.2 inches
Body length: 12.8 inches
Body diameter: 4.2 inches
Wall thickness: 0.57 inches
Tail length: 7 inches
Tail width: 6.5 inches
Tail weight: 2.5 pounds
Filling: Cast TNT
Weight of filling: 4.5 pounds
Total weight: 33.4 pounds
Charge/weight ratio: 13%

Body construction: Cast-steel nose and tail pieces are threaded onto a tubular steel body.  The only difference in construction is that in the Mk 5 Mods 1 and 2, 23 rings cut from seamless tubing are fitted around the tubular body, while on the Mk 5 Mod 3, a steel wire is helically wound left-handed, the adjacent surfaces of wire being parallel.


Suspension: Horizontal suspension is provided by a single eyebolt which is screwed into a ring at the center of the body.


Color and markings: Yellow overall or grey with yellow disc on the body.


Tail construction: Four sheet metal vanes are welded to the tail cone, which is secured to the base plug by a single bolt.

5-pound A.A. Mk 34 (Obsolete) and 3-pound Type C Mk 32 (Obsolete)

No picture available

Mk 34

Overall length: 15 inches
Body length: 12 inches
Body diameter: 3 inches
Wall thickness: 0.05 inches
Tail length: 3 inches
Tail width: 3 inches
Filling: TNT
Weight of filling: 1.9 pounds
Total weight: 5.5 pounds
Charge/weight ratio: 34.5%

Body construction: The reinforced steel nose and conical tail section are welded to a cylindrical steel body.


Suspension: The container Mk 3 or Mk 3 Mod 1 is used.  Its capacity is 20 Bombs Mk 34.


Color and markings: The bombs are painted grey or olive drab overall.  If grey, they will have a yellow disc on the body; if olive drab, they will have a yellow nose band.


Tail construction: Eight sheet-steel vanes are welded to a tail cone which, in turn, is welded to the body.  The vanes are welded on the cone at a ten-degree angle from the longitudinal axis.


Remarks: The 3-pound A.A. Bomb Type C (Mk XXXII) is a smaller copy of the 5-pound Bomb Mk 34.  It is no longer being used.

Bomb Container Mk 3 Mod 1

Overall length: 51.1 inches
Diameter: 13.2 inches
Capacity: 20 A.A. Bombs Mk 34

Mk 3
Weight (Unloaded): 65 pounds
Weight (Loaded): 175 pounds

Mk 3 Mod 1
Weight (Unloaded): 67 pounds
Weight (Loaded): 177 pounds

General: The containers are designed to carry 20 A.A. Bombs Mk 34, ten in the front compartment and ten in the rear.


Description: Each housing assembly contains three bomb bays running lengthwise, the outer side holding three bombs each, and the center holding four bombs; a total of ten for each assembly.  The bombs are loaded onto three ejector springs that run crosswise of the housing and are anchored on the flange on each side of the housing.  These springs eject the bombs after the door-opening mechanism unlatches the doors.  After the last bomb has left each compartment, the door-closing mechanism shuts and holds the doors closed under spring tension until the container is re-loaded.  The skin of the container is of sheet aluminum.


Operation: When the operating switch is closed, the Solenoid Mk 24 or Mk 24 Mod 1, mounted on each of the door-opening assemblies, is energized.  The solenoid unlatches the doors.  The ten bombs in the front compartment are expelled on the first closing of the operating switch, and the ten in the rear are expelled on the second closing of the switch.  The container can also be operated manually.


Remarks: The Bomb Containers Mk 3 and Mk 3 Mod 1 are identical, with exception of the suspension band, fork rests, and outside skin.

1,000-pound Aircraft Mine Mk 13 Mod 0, Magnetic Induction;
Mk 13 Mod 3, Magnetic Induction;
Mk 13 Mod 4, Magnetic Induction; and
Mk 13 Mod 5, Acoustic

Overall length: 68.75 inches

Diameter (case): 19.875 inches
Diameter (tail section): 15.25 inches
Diameter (fins on tail section): 25.5 inches

Mods 0, 3, and 4 -- TNT
Weight of filling: 640 pounds
Total weight: 1,030 pounds
Charge/Weight ratio: 62%
Negative buoyancy: 430 pounds

Mods 0, 3, and 4 -- Torpex
Weight of filling: 700 pounds
Total weight: 1,090 pounds
Charge/Weight ratio: 63.3%
Negative buoyancy: 490 pounds

Mod 5 -- TNT
Weight of filling: 640 pounds
Total weight: 1,000 pounds
Charge/Weight ratio: 64%
Negative buoyancy: N/A

Mod 5 -- Torpex
Weight of filling: 700 pounds
Total weight: 1,060 pounds
Charge/Weight ratio: 66%
Negative buoyancy: N/A

General: The Aircraft Mine Mk 13 Type is designed as a ground influence mine, laid offensively by aircraft from altitudes of 100 to 500 feet in 16 to 75 feet of water (40-100 feet for Mk 13 Mod 5) against surface craft and up to 500 feet against submarines.  The Aircraft Mines Mk 13 Mods 0, 3, and 4 are magnetic induction mines using the Search Coil Firing Mechanism M4, while the Mk 13 Mod 5 is an acoustic mine utilizing the Acoustic Firing Mechanism A3.

When the mine is dropped as a bomb, the minimum altitude of release is 1,200 feet to insure pilot safety.  Because of the shape of the mine, the standard bomb nose fuzes require longer air travel to arm.


Mine construction: The body is a cylindrical steel case with a welded hemispherical nose containing a fuze seat liner which houses an adapter ring and two Auxiliary Boosters Mk 1.  The cylindrical tail section is of a smaller diameter and is welded to the body.  The dome steel tail cover of the Mk 13 Mod 5 is modified to contain the Microphone MI-2; the rubber diaphragm microphone cover of the Mk 13 Mod 5 is stamped with the word "BRUSH".  Horizontal suspension is accomplished by either of three sets of lugs placed 45 degrees apart; each set consists of two standard lugs 14 inches apart.


Color: Black overall


Remarks: The extender and clock starter are activated by hydrostatic pressure at a depth of 16 feet or greater.  The clock delay runs off in 45 minutes to arm the mine.

The Aircraft Mine Mk 13 Mod 3 is a Mk 13 Mod 0 fitted with the Tail Parachute Pack Mk 1.

In the Mk 13 Mod 4, the extender and clock starter are modified for shallow-water planting, allowing the mine to function in ten feet of water.  In other respects, the Mk 13 Mod 4 is identical to the Mk 13 Mod 0.

Cluster Adapter Mk 3 Mod 0

General: The Cluster Adapter Mk 3 Mod 0 is used to cluster three bombs for external suspension on V.B.F.-type aircraft.  The purpose of this cluster is to increase the bomb-load capacity of fighter planes.  Five types of bombs may be used with this adapter, as outlined below:

3x 100-lb G.P. AN-M30A1 (Weight: 364 pounds)
3x 90-lb Frag. M82 (Weight: 300 pounds)
3x 220-lb Frag. AN-M88 (Weight: 688 pounds)
3x 260-lb Frag. M81 (Weight: 800 pounds)
3x 100-lb Incendiary AN-M47A2 (Weight: 340 pounds)

The adapter consists of a band incorporating a take-up bolt, a frame assembly, and a delay opening pistol assembly.


Operation: When the cluster is dropped, the arming wires are withdrawn and the pistol and tail fuze vanes are free to rotate.  After approximately 45 revolutions of the vanes, the arming screw will thread far enough out to allow the firing-pin release levers to cam in.  The firing-pin spring, acting through the firing pin on the firing-pin release levers, will cause the upper portion of the firing-pin release levers to cam in.  The lower portion of the firing-pin release levers then releases the firing pin, allowing it to move aft under action of the firing-pin spring, to strike the percussion cap of the caliber .45 blank cartridge.

Explosion of the blank cartridge expels the cartridge chamber and cartridge-chamber plug (as a unit) from the pistol cradle, pulling the two cotter pins out as they are ejected.  The cluster band clamps that were held together by the clamping action between the cartridge chamber and the pistol cradle, and are now free to open.  Through the action of the displacing springs, the three bombs are ejected from the cluster.  The bomb tail-fuze arming wires are withdrawn when the cluster falls from the plane, and the bomb nose fuzes are free to arm after being ejected from the cluster, freeing their vanes from the fuze arming safety plate.

The air-arming delay-opening pistol requires approximately 45 turns to arm, and will allow the cluster to drop approximately ten feet below the releasing aircraft before functioning.  Minimum release altitudes for these clusters are the same as those issued by the Chief of Naval Operations for bombs of the size used and fuzes installed plus twenty-five feet to allow for cluster opening.  These clusters are safe for take-offs and landings anywhere, including catapult take-offs and arrested landing.

Cluster Adapter Mk 4 Mod 0

Bombs: Two 100-pound G.P. bombs

General: The Cluster Adapter Mk 4 is a simplification of the Mk 3.  It employs only the band and pistol release device to hold the bombs together.  With the bombs clustered together, one of them is then suspended from the bomb rack by its suspension lug.  The nose-fuze vanes are held stationary by two clips which are attached to wire springs.  These springs are held between the bombs until the cluster opens, after which they are sprung free.

Cluster Adapter Mk 7 Mod 1

Bombs: Eight 20-lb Frag. Bombs, AN-M41A1

Total weight: 186 pounds

Loaded length: 46.38 inches

Width: 8.36 inches

General: This cluster, 250-pound bomb size, uses the same pistol release device to open the cluster as used on the Mk 3; otherwise the mechanism is different.  In this cluster, there is not only the release of the steel bands holding the bombs together but a spring-loaded force to push the bombs out of the cluster.

Description and operation: The frame has a front and a rear plate separated by the longitudinal members, the upper and lower rods.  The lower rod is rigid, but the upper one is free to rotate.  To this upper rod are fixed the band hooks.  When the cluster is assembled, the hooks are under torque from the tension of the band.  However, the band hooks are held stationary by a king pin swung between two supports, which supports are placed between the upper and the lower rods.  Firing of the pistol device, seated in the front plate, knocks out this king pin, allowing the upper rod and hooks to rotate, freeing the bands.

When the bands fall off, the springs on the lower rod expand and, acting through the lever arms, push outboard on all the bomb cradles, forcing the bombs away from the cluster.

The arming vanes of the nose fuzes in the fragmentation bombs are kept from turning by safety arms attached to the front plate.

The cluster is suspended by the suspension plates in the middle part of the cluster.

Next Time:"AN" Series (Part 1)

American Projectiles and Explosives - Explosive Bombs - Navy "MK" Series (Part 1)

American Projectiles and Explosives



Explosive Bombs

Navy "MK" Series


General

The Navy-designed bombs are generally similar to Army bombs of the same class.  Since the formation of the Army-Navy Standard Board, early in 1941, the Navy has concentrated on designing bombs for naval targets and for carrier handling, leaving the other types of bombs to Army designers.


Color

The Navy formerly used a yellow paint over all; later, grey over all, with a yellow disc painted between the lugs if the bomb is a high-explosive type.  Later productions may be found painted olive drab overall, with yellow bands.

100-pound G.P. Mk 1 Mods 2 and 3, Mk 4 Mods 1-4 (Obsolescent)

Mk 1

Overall length: 48.8 inches
Body length: N/A
Body diameter: 7.9 inches
Wall thickness: N/A
Tail length: 21 inches
Tail width: 9.8 inches
Filling: TNT
Weight of filling: 65 pounds
Total weight: 116 pounds
Charge/weight ratio: 56%

Mk 4

Overall length: 36.2 inches
Body length: 28 inches
Body diameter: 8 inches
Wall thickness: 0.175 inches
Tail length: 9.1 inches
Tail width: 11 inches
Filling: TNT
Weight of filling: 55 pounds
Total weight: 120 pounds (Mod 1) - 195 pounds (Mod 4)
Charge/weight ratio: 45.8% (Mod 1) - 52.8% (Mod 4)

Body construction: Mk 1 has two sheet steel castings welded together, the bomb having a "tear drop" shape.  Mk 4 is a single-piece steel forging; cylindrical, with ogival nose.


Suspension: Mk 1 is horizontally suspended by two lugs welded on the body; it may have single lug or trunnions on the band.  Mk 4 has two lugs welded on the body 14 inches apart; with a single lug welded on the opposite side.


Color and markings: Grey overall with a four-inch yellow disc between the two lugs, indicating H.E.  The color may be yellow overall.


Tail construction: Mk 1 has four vanes which pass down over the body and are welded to a tail cone.  The vanes are fastened to the body of the bomb by screws and are braced by two sets of bar struts riveted to the vanes.  Mk 4 has four vanes welded to a sleeve which is secured to the bomb body with a locking nut.  Box-type internal struts are welded to the vanes.

500-pound G.P. Mk 3 Mod 1, Mk 9, and Mk 12 Mods 0-2 (Obsolescent)

Mk 12 Mod 2

Overall length: 59.5 inches
Body length: 42.6 inches
Body diameter: 14 inches
Wall thickness: 0.36 inches
Tail length: 20 inches
Tail width: 19.4 inches
Filling: TNT
Weight of filling: 256 pounds
Total weight: 504 pounds
Charge/weight ratio: 50%

Body construction: One-piece steel, forged or drawn; cylindrical, with ogival nose.


Suspension: Horizontal suspension by two lugs or trunnions on band for dive bombing.


Color and markings: Grey overall with yellow disc between lugs, indicating H.E.


Tail construction: Four sheet metal vanes are welded to a cone which is attached to the body by a nut which surrounds the fuze.  Box-type struts are used.


Remarks: The 500-pound G.P. Bomb Mk 12 Mod 2 is still to be found in the field, but is no longer being manufactured.  The other Marks are obsolete.  The Mk 12 and Mk 12 Mod 1 differ from the Mk 12 Mod 2 as follows: Trunnions are welded to the body.  They also have two hoisting lugs welded to the body, a female base plate, and a right-angle fin sleeve instead of the conical type.

1,000-pound G.P. Mk 3, Mk 5, Mk 9, and Mk 13 Mods 0-2 (Obsolescent)

Mk 13 Mod 2

Overall length: 72.6 inches
Body length: 53 inches
Body diameter: 17.7 inches
Wall thickness: 0.45 inches
Tail length: 22.3 inches
Tail width: 23.5 inches
Filling: TNT
Weight of filling: 511 pounds
Total weight: 1,005 pounds
Charge/weight ratio: 51%

Body construction: One-piece drawn or forged steel; cylindrical with ogival nose.


Suspension: The bomb is suspended horizontally by two suspension lugs, or by trunnions on the band around the body for dive bombing.  A torpedo sling guide key is welded to the bomb for suspension in torpedo slings.


Color and markings: The bomb is painted grey overall, with an 11-inch yellow disc between the suspension lugs to indicate H.E.


Tail construction: Four vanes welded to the tail cone, which is secured to the body by a locking nut which screws onto the threaded collar of the base plate.


Remarks: Though this bomb may be found in the field, it is no longer being manufactured.

The Bombs Mk 3, Mk 5, and Mk 9 are declared obsolete and will be expended in practice.

The Mk 13 and Mk 13 Mod 1, also declared obsolete, differ from the Mk 13 Mod 2 as follows: Trunnions are welded to body.  There are two hoisting lugs welded to the body, in addition to a single hoisting lug between the suspension lugs.  They have a female base plate instead of the conical type.

1,000-pound G.P. Mk 36

Overall length: 71.2 inches
Body diameter: 18.7 inches
Filling: TNT
Weight of filling: 558 pounds
Total weight: 1,012 pounds
Charge/weight ratio: 55%

General: The 1,000-pound Bomb Mk 36, is a modified version of the 1,000 pound G.P. Bomb, AN-M44.  These modifications provide for the use of Nose Fuzes AN-Mk 219 or Mk 221, the use of Tail Fuzes Mk 223 or Hydrostatic Mk 229 Mod 3, a Navy-type hoisting lug and guide key, trunnions for dive bombing, and an explosive filling of TNT, rather than 50-50 Amatol.


Description: This bomb has two suspension lugs, spaced 14 inches apart, welded to the bomb body for suspension from double-hook racks and shackles.  A guide key is provided on the opposite side of the bomb for sling suspension.


Remarks: The G.P. Bomb Mk 36 was designed primarily by the Navy as an alternate for the 1,000-pound G.P. Bomb Mk 13 Mod 2.

7-inch 100-pound Depth Bomb Mk 52

Overall length: 45.9 inches

Body length: 7 inches
(Note: I believe this should be Diameter, not Length)

TNT
Weight of filling: 45.3 pounds
Total weight: 99.1 pounds
Charge/Weight ratio: 46%

Torpex
Weight of filling: 50.3 pounds
Total weight: 104.1 pounds
Charge/Weight ratio: 49%

General: This is a light-case, fast sinking, round-nose bomb for use by airships.  It is carried in a Bomb Rack Mk 53 and, accordingly, has no trunnions, trunnion bands, or suspension lugs.  A cylindrical shroud is fastened to the tail section by four vanes.  The entire tail assembly is fastened to the rear of the bomb body by six flat-head machine screws.  A cast-iron nose, into which is fitted a booster can, is secured to the bomb body.  The bomb is filled with either TNT or Torpex.  The Nose Fuze Mk 140 will normally function on impact with a solid object below the surface of the water, but will also function upon striking the surface of the water at any velocity greater than approximately 300 feet per second.  This velocity may be attained in a free fall from a vertical height of 1,400 feet.

650-pound Depth Mk 29 (Obsolete) and Mk 37 (Obsolete)

Mk 29

Overall length: 70 inches
Body length: 41 inches
Body diameter: 17.7 inches
Wall thickness: 0.12 inches
Tail length: 36 inches
Tail width: 17.7 inches
Filling: TNT
Weight of filling: 464 pounds
Total weight: 657 pounds
Charge/weight ratio: 70%

Mk 37

Overall length:63 inches
Body length: 41 inches
Body diameter: 17.7 inches
Wall thickness: 0.12 inches
Tail length: 29 inches
Tail width: 17.7 inches
Filling: TNT
Weight of filling: 464 pounds
Total weight: 659 pounds
Charge/weight ratio: 70%



Body construction: These bombs are manufactured with a hemispherical nose reinforced with a steel disc.  The suspension lugs are reinforced with a steel strip.  A flat-nose attachment, in the shape of a bucket and fitting down under the nose of the bomb, can be used to improved underwater trajectory.  The vacant spaces are then filled with plaster of paris.  These attachments increase the weight by 72 pounds.


Suspension: Horizontal suspension is provided by the usual two suspension lugs, with threaded holes on each side 90 degrees removed to receive trunnion lugs for the displacement gear of dive bombers.


Color and markings: The bombs are painted olive drab or grey overall, with an 11-inch yellow disc between the two suspension lugs.  They may be light grey overall.


Tail construction: Four sheet-steel vanes are welded to the tail cone, which is secured to the body by a locking nut screwing onto the rear of the body.  An annular strut is used around the rear of the vanes.  The tail of the Mk 37 was shortened by seven inches so that the Tail Fuze Mk 229 could arm more readily.  Otherwise, the tail is similar to that of the Mk 29.


Remarks: AN-Mk 219 will not arm under 2,500 feet of altitude if the flat-nose attachment is used.

AN-M103 or AN-M103A1 will not arm with the flat-nose attachment, unless special arming vanes are used.

An extender is supplied with each bomb to permit installation of the Hydrostatic Fuze AN-Mk 224 or AN-Mk 234 in the longer athwartships tube.

The Mk 29 is converted to the Mk 37 by replacing the tail.

Because of numerous instances in water crash landings where depth bombs fuzed with the Athwartships Fuze AN-Mk224 or AN-Mk 234 exploded, these two fuzes have been suspended from use.  As a consequence, the Depth Bombs Mk 29 and Mk 37 may be used only if a nose impact fuze is installed.

Next Time: Navy "MK" Series (Part 2)

American Projectiles and Explosives - Explosive Bombs - "M" Series (Part 2)

American Projectiles and Explosives



Explosive Bombs

30-pound Frag. M5 (Obsolete)

No picture available

Overall length: 25.5 inches
Body length: 13.05 inches
Body diameter: 4.2 inches
Wall thickness: 0.6 inches
Tail width: 6.5 inches

Type of filling: TNT
Weight of filling: 4.66 pounds
Total weight: 29.8 pounds
Charge/weight ratio: 16.3%
Fuzing: Mk XIV

Body Construction: The body consists of a seamless steeel tube over which are fitted rings cut from cast-steel pipe.  Cast-steel nose and base pieces thread onto this center tube.


Suspension: The bombs may be suspended horizontally, vertically, or in a cluster.  U-shaped eyebolts are welded to the bomb at the center of gravity and to the rear of the tail.  Later issues of bombs were in the Cluster M3, which contained six 30-pound Frag. Bombs, M5.


Tail construction: Four rectangular sheet-steel vanes are welded to a length of one-inch cast-iron pipe that screws into the base filling plug.

2,000-pound S.A.P. M103

Overall length: 89.29 inches
Body length: 68.5 inches
Body diameter: 18.63 inches
Wall thickness: 1.3 inches
Tail length: 25.6 inches
Tail width: 25.8 inches
Tail weight: 52.7 pounds

Type of filling: Picratol
Weight of filling: 556 pounds
Total weight: 2039 pounds
Charge/weight ratio: 27%

Fuzing: Unlike smaller S.A.P. bombs, the M103 has a solid nose, permitting tail fuzing only.


Construction: The body of the M103 is fabricated from seamless steel tubing, somewhat streamlined in shape and with a semi-pointed nose.  No provision is made for nose fuzing in this bomb.  Suspension lugs are welded tot he case in a manner similar to the G.P. bombs.  Trunnions on a band may be fitted for dive-bombing.  A box-type tail is employed as on the G.P. bombs.


Filling: Picratol, a mixture of 52% Explosive "D" and 48% TNT, is poured as the main charge, with a wax pad in the nose to cushion the explosive against premature detonation on impact with a hard target.


Remarks: The suspension lugs are 30 inches apart.  Suspension bands are under development and will be issued, when available, for installations requiring 14-inch suspension.

4-pound Frag. "Butterfly" M83

Overall length: 3 inches
Body length: 3 inches
Body diameter: 3.1 inches
Wall thickness: 0.25 inches

Type of filling: TNT
Weight of filling: 0.47 pounds
Total weight: 3.2 pounds
Charge/weight ratio: 15%

Fuzing: M129 Air or Ground burst, M130 Time, maximum 30 minutes, or M131 Anti-Disturbance.

Body Construction: The bomb body is cylindrical in shape, cast in two halves and welded together.  The fuze cavity is situated athwart-ships in the body, is 1 and 3/4 inches in diameter, and is threaded with a left-hand thread.  The left-hand thread is to prevent unscrewing of the fuze while the bomb is in flight.


Arming vane assembly: The vane assembly consists of four pieces hinged together - two semi-cylindrical surfaces (wings) and two discs (propeller blades) inclined at a slight angle.  While the bomb is still in the cluster, the vane assembly is folded around the bomb to form a cylindrical casing which can be closed against the pressure of the vane coil springs by means of a safety clip.  The arming spindle projects through the bomb casing.

When the bombs are packed in the cluster adapter, the safety clips are removed by the bombs remain in their closed status because of their proximity to each other.  When the cluster adapter bursts open, the bombs scatter and the vane assembly on each bomb is spread open by the force of its coil springs.  The vane assembly is forced by air resistance to the top of the arming spindle, where the square head on the spindle engages the square hole in the assembly.  The two wings reduce the velocity of descent of the bomb.  The two propellers, being set at angles to each other, case the vane assembly to turn in a counterclockwise direction, thereby screwing the arming spindle out of the fuze body and permitting the fuze to arm.  The arming spindle is not completely withdrawn from the fuze, being retained in the fuze by a collar on the spindle.


Markings: The bombs are painted olive drab, with a half-inch yellow band running horizontally around the folded wings.

90-pound Frag. M82

Overall length: 28 inches
Body length: 19.8 inches
Body diameter: 6 inches
Wall thickness: 0.94 inches
Tail length: 9.3 inches
Tail width: 8.1 inches
Tail weight: 2.8 inches

Type of filling: Composition B
Weight of filling: 12 pounds
Total weight: 91.6 pounds
Charge/weight ratio: 13.1%

Construction: Nose and tail pieces of cast steel screw onto a central section of seamless steel tubing.  A square helical steel spring is wound around the steel tubing.  The nose and tail pieces are partially cut through, to afford greater fragmentation.  The bomb is suspended by single lug or in a cluster (M27) of six bombs.  The tail is of normal U.S. box construction and is secured to the bomb by a locking ring.

120-pound Para-Frag. M86

Parachute container length: 35.5 inches
Diameter: 6.5 inches


Description: The M86 consists of the 90-pound Fragmentation Bomb M82, and a Parachute Unit M5 which is screwed to the base of the bomb body in place of the normal tail fin assembly.  Both units are issued separately and must be assembled prior to use.

The Parachute Unit M5 consists of a cylindrical container housing the parachute.  The lid of the container is fastened by a latch, which is secured by the arming wire.

The bomb is fuzed with the Fuze AN-M120 or AN-M120A1 by using the Adapter Booster M117.

Suspension: The bomb can be used ina  bomb station having the clearance of a 500-pound bomb, and may be suspended singly or as a two-bomb cluster with the Cluster Adapter M12.  One suspension lug is welded to the bomb at the center of gravity, and two suspension bands are issued with the parachute unit.  The larger-diameter band is secured on the parachute unit to be used in conjunction with the suspension lug or the smaller-diameter band secured on the bomb body.


Operation: Thea arming wire, which is fastened to the bomb shackle, passes through the lug of the rear suspension band and the latch on the parachute container, but not through the fuze.  This secures the latch and prevents the parachute from opening until immediately after release of the bomb.  The arming wire which passes through the fuze is fastened to the parachute by the arming cord.

On release, the arming wire is withdrawn from the latch on the container.  As the bomb falls, the air stream removes the lid from the container and allows the parachute to open.  The arming cord is attached ot the shroud line and is pulled as the parachute opens, thereby permitting the fuze to arm.

Fragmentation Bomb Clusters

M1 - Adapter M1

100-pound size for six 20-pound Frag. Bombs AN-M41.  It is 46.75 inches long and weighs 125 pounds.  It has lugs for double-hook suspension only.  The release mechanism operates by means of a cartridge and firing mechanism.



M27 - Adapter M14

500-pound size cluster for six 90-pound Frag. Bombs M82.  The adapter consists of two longitudinal steel tubes, 56 inches long, to which are welded four steel plates forming the support for the six bombs.  The lower tube serves as the backbone of the cluster; and the upper tube carries the suspension lugs, the buckles for the releasing straps, and the adapters for the nose and tail fuzes.  The Nose Fuze M111A2 or M155 is used; however, there is no mechanical time fuze in the tail.

The cluster may be adjusted to release the bombs immediately or, through the use of mechanical time fuzes, to discharge the bombs 5 to 92 seconds after the release of the cluster from the plane.  If it is intended that the cluster is to open immediately, the shear wire is cut after the arming wire is installed, and no fuze is used.  The immediate opening of the cluster produces the most favorable impact pattern.  The cluster must open at a minimum altitude of 1,000 feet in order that the bomb fuze may arm.

M28 - Adapter M15A1

100-pound size for twenty-four 4-pound Frag. Bombs M83.  It is a cylindrical sheet-metal case, which opens longitudinally, being hinged at the rear and closed by a nose cup.  It is 47.35 inches long and 8 inches in diameter, and weighs 155 pounds loaded.  It uses Fuze M155 or AN-M146.

These clusters are released from altitudes of not less than 3,000 feet and not more than 5,000 feet.  Fuze settings for function after release are varied from five seconds at minimum release altitude to eight seconds at maximum release altitude.  When the fuze fires, it releases the nose closing cup, allowing the adapter to open and release the bombs.  The bombs scatter to form a pattern over an area of approximately 300 by 200 feet.

M28A1 - Adapter M15A1

The Cluster M28A1 is the same as the M28, except that it incorporates a spoiler ring around the nose and a drag plate secured ot the tail by four screws.  These two devices were added because the dropping altitude for the M28 was limited by the high velocity attained by the clusters at high altitudes, resulting in damage to the butterfly when the cluster opened.  When drag plates and spoiler rings are used, the recommended release altitude is 1,500 feet with a six-second fuze setting, or any high altitude which will open the cluster at a height between 1,000 to 2,5000 feet.

M28A2 - Adapter M15A2

This A2 modification has a new locking cup, which is secured to the adapter by two slotted screws.  Otherwise, it is the same.

M29 - Adapter M16A1

500-pound size for 90 4-pound Frag. Bombs M83.  The container is like the M15, except for size.  In the Adapter M16, the bombs are loaded in "wafer" assemblies.  This cluster has a third single lug for British suspension.

M29A1 - Adapter M16A2

This A1 modification has the new locking cap, secured to the adapter by two slotted screws.  Otherwise, it is the same.

Remarks

For Navy usage, the Bureau of Ordnance recommends that the case-locking bushing it has developed be used with all "Butterfly" fragmentation clusters, including the M28, M28A1, M28A2, M29, and M29A1.  One end of the bushing screws into the fuze adapter, and the other end is threaded internally to receive the fuze.  The locking cup is retained positively by a safety wire which passes through a hole in the locking-cup tab and around a cotter pin placed int he bushing.  When the fuze fires, the locking cup is blown into the cluster, shearing the loops of safety wire and allowing the adapter to open.

Next Time: Navy "MK" Series (Part 1)