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)