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| BRITISH EXPLOSIVE ORDNANCE |
| Part 1 - Chapter 10 |
| Buoyancy Bombs |
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B. 250-lb. Mk IV (Service) |
| Data |
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Fuzing |
Tail Fuze No. 850 |
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Color markings |
Dark grey over-all; ½-in. red band 3 in. from nose; ½-in. green band 9½ in. from nose |
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Tail No. |
No. 23 Mk I with the Mk III body |
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Over-all length |
72 in. |
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Body length |
42 in. |
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Body diameter |
14.3 in. |
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Tail length |
28 in. |
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Tail width |
14.3 in. |
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Total weight |
250 lb. (approx.) |
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Charge/weight ratio |
40% (approx.) |
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Body Construction: The bomb consists of a truncated, cone-shaped charge case with a concave nose welded on, a buoyancy chamber secured to the charge case by twelve nuts, and a clip-on tail. A convex nose attachment can be fitted to the nose by means of three brackets, equi-spaced around the edge of the nose. The buoyancy chamber has twelve hand clearance pockets around the forward end to permit access to the twelve bolts securing the charge case. Internal reinforcements are spot welded to the interior forward half of the buoyancy chamber, and two circular stifferener extend athwartships through the chamber, spot welded to the chamber wall. An exploder tube extends centrally the buoyancy chamber and charge case. It is welded at the rear to the joint ring fitting inside the fuze pocket, and supported by the stiffening ring in the middle of the buoyancy chamber. |
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Tail Construction: The Tail No. 23 Mk I, used on the Mk III body, consists of a tail cone with cylindrical strut secured by four fins riveted to the strut and tack welded to the tail cone. The tail assembly is attached to the body by spring clips, and breaks free on water impact. |
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Functioning: On striking the water, the nose attachment is dished in and the tail breaks away. When the tail breaks away, it uncovers a wheel-shaped disc on the base of the bomb. This is the contact disc, to which are attached three chains, the opposite ends being fastened to the support ring on the bomb base. If these chains are tight, the fuze is armed as the contact disc rises during the arming process. If the bomb fails to hit a ship upon rising, it sinks after a short flotation period. |
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Suspension: The bomb is suspended by a single lug secured by four screws threaded into a suspension-lug stiffener, and a boss, spot welded to the interior of the buoyancy chamber. |
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Explosive Components |
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Exploders – C.E. exploders in central tube. |
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Filling – 113.2 lb. Torpex 2, with 3.25 lb. TNT topping in after end of charge case |
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Remarks: This bomb is designed to be dropped in front of ships under way, and to rise and detonate on contact with the ship's bottom. The concave nose portion of this bomb is designed to give better under-water ballistics, rather than a Munroe effect. |
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Figure 36 - B. 250-lb. Bomb Mk IV |
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