pzgr40
Well-Known Member
Cutaway models of WW2 British smoke bombs as used for aircraft usage. Both are used in clustered bomb versions, either 90pcs 4 lb bombs in five tiers of 18 bombs each, the 2lb in a small bomb container or a cluster adapter with a (to me unknown) number of 2 lb smoke bombs (pict 04 & 05).
In both cases the bomb consists of a sheet metal body. With the 4 Lb it is filled with 3 ¼ Lb SR264 A smoke composition, topped with ¼ Lb SR 269. The ignition charge consists of a black powder igniter pellet, topped with a primed cambric strip for ignition by the stab detonator of the No 859 fuze.
I do not know exactly what the charge for the 2 Lb smoke bomb is , but I assume the smoke composition build-up will be approximately the same.
Some more info can be found in this posting :
2lb Smoke Bomb ???? (bocn.co.uk)
It is also the source where I got the two pictures of the cluster adepter from, taken by US Subs.
For both smoke bombs:
Description and functioning of the No.859 all-ways fuze:
A sensitive open stab detonator (red) is placed in a hard lead cylinder with a chamfered edge on the side of the firing cap. A channel is drilled through the cylinder, housing the firing pin. The firing pin has a disc in top with a chamfered edge towards the centre. A lead ball is placed in this disc. A radial hole is drilled through the firing pin, blocking it from inward movement toward the stab detonator if the safety pin is stuck through. The safety pin is connected to a linen tape with a curved lead weight at the other end. The firing pin is kept away from the stab detonator by a weak creep spring.
The hole in the Bakelite fuze housing in which the fuze assembly is placed also has two chamfered edges in top and bottom.
When packed in the small bomb container (4lb) either a cluster adapter (1Lb) the Bakelite caps on the fuzes are fixated by their bulkheads, fixating them from being accidentally removed from of the fuze body before release from the small bomb container, either before activation of the cluster adapter after it is dropped. After release/ drop the fabric strip on the Bakelite cap catches the airstream and pulls of the cap. The linen ribbon with the lead weight unrolls, pulling the safety pin from the grenade during flight. The grenade is now armed.
It does not matter in which position the smoke bomb lands:
-Perpendicular on base: inertia will push the lead ball with the firing pin down into the firing cap.
-Perpendicular on the fuze: inertia will push the firing cap cylinder into the firing pin.
-Landing on its side or any angle: The ball, either the firing cap housing -either both- will be swung to the side due to inertia, moving along the chamfered edges of the fuze housing. This will change a sideways movement into a linear one, pushing the firing pin into the stab detonator, allowing the firing pin to ignite the firing cap.
It must be noted that the No. 859 all ways fuze is a modification of the No.247 all ways fuze as used on the Bakelite No.69 grenade. The difference is that the No.859 has no thread on the inside of the safety cap and falls off as soon as the smoke bomb is rotated, as the safety cap with the No.247 has to be unscrewed fom the fuze, and the thumb has to be placed on the lead weight before the grenade is thrown.
4Lb Mk2 :
Length : 197mm
Diameter : 90mm
Length bomb body : 162mm
2Lb :
Length : 147mm
Diameter :59mm
Length bomb body : 113mm
Regards, DJH
In both cases the bomb consists of a sheet metal body. With the 4 Lb it is filled with 3 ¼ Lb SR264 A smoke composition, topped with ¼ Lb SR 269. The ignition charge consists of a black powder igniter pellet, topped with a primed cambric strip for ignition by the stab detonator of the No 859 fuze.
I do not know exactly what the charge for the 2 Lb smoke bomb is , but I assume the smoke composition build-up will be approximately the same.
Some more info can be found in this posting :
2lb Smoke Bomb ???? (bocn.co.uk)
It is also the source where I got the two pictures of the cluster adepter from, taken by US Subs.
For both smoke bombs:
Description and functioning of the No.859 all-ways fuze:
A sensitive open stab detonator (red) is placed in a hard lead cylinder with a chamfered edge on the side of the firing cap. A channel is drilled through the cylinder, housing the firing pin. The firing pin has a disc in top with a chamfered edge towards the centre. A lead ball is placed in this disc. A radial hole is drilled through the firing pin, blocking it from inward movement toward the stab detonator if the safety pin is stuck through. The safety pin is connected to a linen tape with a curved lead weight at the other end. The firing pin is kept away from the stab detonator by a weak creep spring.
The hole in the Bakelite fuze housing in which the fuze assembly is placed also has two chamfered edges in top and bottom.
When packed in the small bomb container (4lb) either a cluster adapter (1Lb) the Bakelite caps on the fuzes are fixated by their bulkheads, fixating them from being accidentally removed from of the fuze body before release from the small bomb container, either before activation of the cluster adapter after it is dropped. After release/ drop the fabric strip on the Bakelite cap catches the airstream and pulls of the cap. The linen ribbon with the lead weight unrolls, pulling the safety pin from the grenade during flight. The grenade is now armed.
It does not matter in which position the smoke bomb lands:
-Perpendicular on base: inertia will push the lead ball with the firing pin down into the firing cap.
-Perpendicular on the fuze: inertia will push the firing cap cylinder into the firing pin.
-Landing on its side or any angle: The ball, either the firing cap housing -either both- will be swung to the side due to inertia, moving along the chamfered edges of the fuze housing. This will change a sideways movement into a linear one, pushing the firing pin into the stab detonator, allowing the firing pin to ignite the firing cap.
It must be noted that the No. 859 all ways fuze is a modification of the No.247 all ways fuze as used on the Bakelite No.69 grenade. The difference is that the No.859 has no thread on the inside of the safety cap and falls off as soon as the smoke bomb is rotated, as the safety cap with the No.247 has to be unscrewed fom the fuze, and the thumb has to be placed on the lead weight before the grenade is thrown.
4Lb Mk2 :
Length : 197mm
Diameter : 90mm
Length bomb body : 162mm
2Lb :
Length : 147mm
Diameter :59mm
Length bomb body : 113mm
Regards, DJH
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