What purpose was the British 40 lb GP HE Bomb for

[Fatboy Coxy]

It was produced between 1937 and 1941, and I'm fairly sure both the Fairey Battle and Bristol Blenheim carried them.

Was it a anti-personnel, fragmentation bomb, or something else?

 

[Wurger]

The General Purpose High Explosive 40lb anti-personnel / fragmentation bomb

British Explosive Ordnance - General Purpose Bombs

British Explosive Ordnance Introduction General Purpose bombs are heavy-cased bombs ranging in weight from 40 pounds t...

ww2data.blogspot.com

Bombs and Fuzes, Section II: British Bombs; G.P. 40 lb. Mk. I, II & III G.P.-H.E. (Stabilized) und G.P. 40 lb. Mk. I, II & III G.P.-H.E. (Parachute equipped)

michaelhiske.de

 

[Greyman]

The requirement that eventually led to the 40-lb GP bomb called for the attack of:

• Billets of the normal dwelling-house type/huts
• Motor transport convoys
• Tanks
• Aircraft on the ground in the open
• Static transformer stations in the open
• Dumps of chemical warfare material

Almost every British bomb-carrying aircraft hauled them at some point.

 

[Fatboy Coxy]

Oh that great guys, thank you.

Both the Battle and Blenheim carried a 1,000lb bomb load internally, made up of four 250lb bombs. I'm reading the 40lb bombs were carried in SBC's (small bomb containers), six making 240lb, and replaced a 250lb bomb. Was the container dropped, and the small bombs released from that, or was it just a fitting allowing the six bombs to be attached to one 250lb bomb fixture.

 

[Greyman]

The latter. The SBC stayed with the aircraft and just the bombs were released.

Good image posted recently:

The smaller bombs could also be carried externally on a LSC (light series carrier).

 

[Wurger]

 

[GrauGeist]

There's several good photos out there that show how the containers were situated in the bomb bay.

Here's one such photo that shows the arrangement in a Lancaster:

(image source: interwebs)

 

[Wurger]

 

[Fatboy Coxy]

six 40 lb bombs in one container, were they all released at the same time, and if so, what kind of radius of destruction would this deliver?

 

[Greyman]

They were released one compartment at a time. So in the case of an SBC loaded with 6 x 40-lb GP bombs, three bombs would drop per press of the firing switch (per SBC selected).

I don't think I have any information on general effectiveness vs. distance from burst.

Observed fragmentation in testing (TNT-filled version) was:

Weight Group (oz)​	Number of Fragments​
.04 - .25​	887
.25 - .5	189
.5 - 4	204
4 - 8	7.5
over 8	0.5

Fragment velocity was 4200 fps

Even a direct hit was useless vs a tank.

 

[Fatboy Coxy]

Oh boy, the longer this thread runs, the more I reveal my ignorance. So on a Battle, and maybe even the Blenheim, I had a (now very stupid) expectation that there was simply a bomb release, and away went the lot. but now I realise that wasn't so. Now a Battle could carry four SBC's in its internal bomb bay, suggesting to me of eight bomb release switches/buttons/levers. was there a dedicated panel for all of these?

 

[GrauGeist]

Someone may have better details, but I suspect the bomb container(s) were configured like an American bomber in that each compartment in the container had a relay that acted like the bomb station release.
In other words, when the commamd to release was given (release button pressed) the first bombs fell away, which triggered the next station's relay, which in turn saw those bombs fall away, triggering the next station in line's relay and so on, until the full release cycle was completed.

 

[Fatboy Coxy]

Someone may have better details, but I suspect the bomb container(s) were configured like an American bomber in that each compartment in the container had a relay that acted like the bomb station release.
In other words, when the commamd to release was given (release button pressed) the first bombs fell away, which triggered the next station's relay, which in turn saw those bombs fall away, triggering the next station in line's relay and so on, until the full release cycle was completed.

Hi GrauGeist, thank you for this, but can I just ask for a bit more detail. A Battle could have a mix of bombs, say a couple of 50 lbs bombs and two SBCs. Would they have to wired them in a predetermined bombing plan for the raid, not allowing the bomb aimer a choice of selection?

 

[stona]

I don't believe there was any switching in the SBC.

When the distributor was set to 'container' all the stations released simultaneously, at least on the Mk VI bomb distributor (intervalometer to the Americans).

 

[Fatboy Coxy]

I don't believe there was any switching in the SBC.

When the distributor was set to 'container' all the stations released simultaneously, at least on the Mk VI bomb distributor (intervalometer to the Americans).

Ok, so regarding strategic bombing, all film I have seen is of a steady release of bombs over several seconds. No doubt this helped provide a spread or carpet. However, light bombers, carrying say four bombs, or SBC's, would want the option of a second run at a target, releasing two at a time. How would they have released their bombs?

 

[stona]

Ok, so regarding strategic bombing, all film I have seen is of a steady release of bombs over several seconds. No doubt this helped provide a spread or carpet. However, light bombers, carrying say four bombs, or SBC's, would want the option of a second run at a target, releasing two at a time. How would they have released their bombs?

Bombs could be released at pre-set intervals, using the bomb distributor. I don't believe that there was any way of releasing bombs from a SBC in anything but one go, given how the containers worked.

 

[Greyman]

As per the manual it is as I described;

'... released one compartment at a time. So in the case of an SBC loaded with 6 x 40-lb GP bombs, three bombs would drop per press of the firing switch (per SBC selected)'.

I'll try to get an excerpt later.

 

[Fatboy Coxy]

It may well be different aircraft were configured in different ways regarding bomb release, I think I need to look more closely at the Fairey Battle, Bristol Blenheim, Vickers Vildebeest and Lockheed Hudson.

 

[Greyman]

I'll try to get an excerpt later.

The electrical system of the container itself is identical for both electrical and mechanical fuzing and comprises an auto-selector switch and four electro-magnetic release units which control the drop bars.

The auto-selector switch becomes energised and one release unit is operated each time the aircraft firing switch is pressed, the next unit for release being selected automatically as the firing switch is released.

At the first operation of the firing switch the auto-selector switch opens release unit No.1; at the second operation unit No.2 is released; at the third operation unit No.3 is released and at the fourth pressing of the firing switch No.4 unit is released.

AP1664 Vol 1 Chapter 3
THE 250 LB. CONTAINER FOR SMALL BOMBS