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| BRITISH EXPLOSIVE ORDNANCE |
| Part 1 - Chapter 11 |
| Incendiary Bombs |
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I.B. 4-lb. Mks I, IE, II, IIE, III and IIIE, and 4-lb. "X" with 2- and 4-minute delays, Mk I (Obsolescent) |
| Data |
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Fuzing |
Integral simple impact striker |
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Color markings |
Mks I-III have dull red nose, with two ½-in. black bands se-parated by ½-in. bright red band around nose. Mks IE-IIIE also have bright red tail base and additional ½-in. bright red band ½ in. abaft dull red nose coloring. |
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Over-all length |
21.4 in. |
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Width across flats |
1.67 in. (hexagonal in shape) |
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Total weight |
4 lb. (approx.) |
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Description: The Bomb Mk III consists of a hollow, magnesium-alloy body, at one end of which is cast iron or steel nose; the body being cast onto the nose during manufac-ture. A magnesium-alloy tail plug, which may be of solid or open construction, is screwed into the other end of the body. Fixed to the tail plug by two drive-screws is a tin-plate tail closed by a tail cap. |
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The tail plug houses a striker, creep spring, ferrule having four tabs, and a brass cap holder containing a 1.7-grain detonator. When the bomb is packed in its case, movement of the striker towards the detonator is prevented by a spring-loaded safety plunger hou-sed in a sleeve fitted into the tail plug. Two vent holes, plugged by cork inserts, are pro-vided in the body to communicate with the space between the cap holder and the filling of the bomb. A strip of primed cambric is located in this space. The Mk IIIE is identical to the Mk III, except for a black powder exploder charge, just abaft the nose plug in the body cavity, which replaces a small quantity of the thermite filler. |
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Functioning: When the bomb is released, the safety plunger springs out. On impact, the striker overcomes the resistance of the creep spring, bends the tabs on the striker support (brass cross), and strikes and fires the detonator. The products of combustion from the detonator blow the cork inserts out of the vent holes. The flash from the deto-nator is conveyed by the primed cambric strip to the priming paste (gunpowder-shellac paste) on the inside of the washer, which ignites the pressed priming composition and in turn the thermite pellets. The magnesium-alloy body starts to melt about 25 sec. after the bomb is ignited, and burns for about 10 minutes. In the Bomb Mk IIIE, after 1½ to 4 minutes, the poder in the burster is ignited and explodes. |
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Suspension: The bombs are carried in the Small Bomb Container, or in a Cluster Pro-jectile. |
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Filling: The bombs are filled with thermite incendiary pellets and the priming pellets which ignite them. The incendiary material from which the bodies are manufactured, a magnesium alloy, also contributes to the incendiary effect. The "E" bombs have an added black-powder burster charge, while the "X" bombs have a C.E. burster. |
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Remarks: The I.B. 4-lb. Mks II and IIE are similar to the Mk III and Mk IIIE, but have the following differences. The bomb bodies have a smaller bore, and the bomb bodies have four cork-plugged vent holes. The tail plugs and cap holders are of solid magnesi-um-alloy, and the noses are of steel. |
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The 4-lb. Bombs Mks I and IE are similar to the Mks II and IIE respectively, but have only a 1.62-grain detonator and are 21.4 in. long. |
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The 4-lb. X, with 2- and 4-minute delays, Mk I is similar in construction to the Mk II, except that a C.E. exploder is contained in the steel nose plug; this exploder being initi-ated after delay of either two or four minutes. The letter "X" is stamped on the outside followed by a number "2" or "4" indicating which delay is incorporated in the bomb. The marking bands are the same as on the Mk IIIE, except that the red band between the two black bands is 1 in. wide instead of ½ in., and the base of the tail is not painted red. |
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Figure 37 - I.B. 4-lb. Mk III |
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Figure 38 – I.B. 4-lb. "X" with 2-minute delay, Mk I |
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