Fuzing bombs for skip-bombing.

[Maxrobot1]

The dud rate for aerial bombs in WW2 has been estimated at around 10% and a recently posted video by "WW2 US Bombers"
View: https://www.youtube.com/watch?v=H1p25U0OZW8 has comments regarding U.S. bomb tail assemblies sometimes separating during the drop and causing the bombs to tumble and "Keyholing" of striking the ground broadside instead of nose first.
This is blamed for some bombs not going off.
When the USAAF developed skip bombing in the Pacific, did they uses special fuzes? I think they did not install tail fins too.
Anybody have ideas?
Watching the video, I had no idea that the Germans saved the fuzes they removed from our duds.

 

[SaparotRob]

Me neither.

 

[Greg Boeser]

Bombs fused for skip bombing had a 4-5 second delay fuse. This would give the aircraft enough time to clear the target before the bomb went off. The bomb would either penetrate the side of the ship, or strike the side then sink before detonating. The resulting overpressure could crack the keel of the ship.

 

[Thumpalumpacus]

Just winding up my physics brain, at 100' ASL there's not a lot of time for the tail to separate or the bomb to tumble, so the bomb is still going to hit roughly horizontal and then skip.

I'm not aware of any removal of tail-fins on the bombs for this sort of delivery. It could be that some separated upon waterstrike, but I've also heard reports of bombs skipping along about the pace of the airplanes and presenting a danger to them.

I think that a tailless bomb would be less likely to skip accurately, but I ain't sure.

 

[hw97karbine]

AT-11 trainers skipping bombs in training:

As you can see these dummy bombs remain more or less nose first but you can't rely on that in practice, not to mention the risk of the bomb detonating on the first impact with the water. A delayed fuze was the most feasible option for such a scenario.

Here is an example of a Japanese fuze designed for such use: JapaneseType 4 "Skipping-Bomb" Tail Fuze - Inert-Ord.net

Note it is an "all ways" fuze that is initiated by the first impact with the water regardless of the orientation of the bomb.

 

[alsaad]

US used AN M112 series fuzes for skip and dive bombing. Fuzes had 7-11 sec delay and were extremely sensitive if unexploded. Bombs had regular box tail assembly.

 

[Maxrobot1]

The M38 water & sand filled dummy bombs in the video clip came with the tail assembly welded on, it was not removable.
In WW2 Bombers video comments, several people mention high-altitude bomb drops in which the tail fin assembly dis-attaches. I have not observed this. However an aerial bomb dropped at 20,000 feet with no stabilizing tail fin had a good chance of tumbling in flight and thus striking the ground broadside instead of nose first.
The video cites German records indicating they recovered un-exploded bombs that did not strike nose-first and so the fuze was not activated.
As a side note, I can easily imagine the ground crew at a bomber base in England getting last minute word on the mission and bomb loads, thus hustling to get the bombs out of storage, to the plane (a mile or two away) then screw on the tail assembly, attach the shackles,crank the bombs up into dark bomb bay, secure them and then someone had to squeeze in there and check the fuzes and attach the arming wires securely. The fuzes could have been installed before hoisting or after secured.
I can imagine the crew chief saying "Take your time - but hurry up."
Mistakes could be made. At least one B-17 blew up on the ramp as the ordnance was being loaded.
I wonder if the fuel tankers had to stand off while the bombs were loaded? The same for refilling the Oxygen system or rearming the guns.

 

[MIflyer]

Well, generally speaking they did not actually skip the bombs off the water but rather slung them into the side or onto ships. I think fusing bombs that were supposed to skip, like a flat stone on a pond, would be very difficult with WW2 technology.

The results in the Battle of the Bismarck Sea were very impressive, the hit rate being up around 70%. They sank every cargo ship and the convoy commander's destroyer. Two weeks later it got worse. A B-17 attacked a IJN cruiser and left it dead in the water just outside of Rabaul ; there was no place the IJN was safe.

The RAF found that rockets designed to penetrate tanks would not, but did a nice job punching through ships and submarine hulls. The trick was to aim at the water right next to the ship and the rocket would hit the water and then turn horizontal underwater. They also found that the rockets with the large explosive charges did a good job on tanks, since they tended to blow the treads off rather than penetrate the armor. So the antitank rockets became antiship rockets and the antiship rockets became antitank rockets.

In the Falklands war the RN found that many of the British bombs dropped by Argentine Air Force A-4's did not detonate and since they knew a great deal about them, disarming them was pretty easy. But the attacks by Argentine Navy A-4's, using American bombs, were far more devastating. Presumably the Navy was using bombs designed for ship attack and thus had better fusing.

 

[Geoffrey Sinclair]

Webster and Frankland, using the USSBS report for oil targets bombed during 1944/45 have a breakdown on the dud or unexploded bomb rate, it varied over time but figures noted were

18.9% RAF origin
12.2% USAAF origin
24.0% Unknown origin

"The main cause does not seem to have been due to faulty fusing but to the fact that the tails of the bombs broke away so they fell flat."

When the USSBS went out and counted the bombs dropped on several German oil targets they found overall around 14% failed to explode, the investigators were shown dumps of allied UXBs. The RAF dud rate was higher than the USAAF one in the sample. Seems badly assembled bombs would not drop straight or would lose their tails, some Germans actually asked the US investigators post war what experiments were the allies doing with tail less bombs, which gives an idea of how often it happened. Add bombs not fitted with fuses, or not properly filled with explosives or where the safety pins were left in before you begin to talk about faulty fuses.

 

[Maxrobot1]

Bombs are ammunition

EOD, Have dug for many a bomb in sand and dirt and found that it not only had the fins attached, it looked like it came from the factory. Also have seen them skip and have very little wear on the paint or fins. My point in this, though, is that the first two bombs have Mechanical Impact Fuzes...

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