Conventional bomb fusing (Read 517 times)

From Bobski - Pat P.

Bruce Gordon wrote:
Bob - my comments on the fuzing shown on the WW II photos that you sent out. You may send this on the group if you think it's interesting...

Here is the photo of those fuze extenders in WW II (it may have been the Korean War in this photo). They are connected IN FRONT of the arming propeller on the fuze, and are a light steel rod. In Vietnam, we used larger pipe with the arming propeller and fuze at the front of the pipe. The fuze struck the ground while the bomb was still three feet in the air, and the fuze blast went up through the pipe and exploded the bomb while it was above the ground. If we wanted the bomb to penetrate a hard target, we did not use fuze extenders. Often we used two fuzes - one in front of the bomb, and one in the tail. We could set the tail fuze for a delay, so we could get the bomb to penetrate several feet into the ground before it exploded, to destroy hard bunkers. The pilot could arm the nose or the tail fuze (or both) to get the bomb to explode on the surface, or deep in the ground, depending on the target that he encountered on the mission.

In the photo below (WW II or Korea) I do not see any arming wires running thru the fuze propellers, so the bombs might arm as soon as the aircraft took off. That is not as safe as in Vietnam, where we had an arming wire running thru the fuze propellers, and the arming wire went to a solenoid in the bomb rack. The wire poked thru the propeller, keeping it from turning. If the bomb fell off (or was jettisoned without arming), the solenoid was not powered and the wire fell with the bomb, so the propeller never turned and the bomb never armed. When the pilot armed the bombs, he put electrical power to the solenoid, which held the wire to the bomb rack. When the bomb fell away, the wire pulled away from the fuze propeller. The wire stayed with the airplane, allowing the fuze propeller to turn in the air and arm the bomb.

If the bomb is not armed when it drops, it does not go off. I was surprised that you could drop a bomb from many thousands of feet altitude onto firm ground and it would not explode!

Secondary things what we did with fuzing. Sometimes bombs explode as soon as they are armed, so we could set the time the propeller had to turn to arm the fuze. We usually set it to 4 seconds after bomb drop, so the bomb was well clear of the fighter before it armed. If we were dropping bombs from low altitude, the bombs might hit the target in less than 4 seconds, so we set the bombs to 2 1/2 seconds to arm. Not as safe, and we could feel the shock wave from the bomb blast hitting our planes, but at least the bombs would explode.

Go forward in time to 1982, to the Falklands War between Argentina and Britain. Argentina had French Mirage and US A-4 Skyhawk fighters, which attacked the British ships unloading troops in a bay in the Falklands. Seven Argentine bombs hit British ships but did not explode. Some of the bombs went completely through the British ships, and some bombs stuck between decks deep in the ships. Several of the British ships survived because the bombs did not explode, although some sank slowly because of the holes made through the ships or because of fires set by the bomb impact - even when the bombs did not explode. Hundreds of British sailors survived because the bombs did not explode.

Someone commented to a reporter that the Argentines were probably using the 4-second delay on their bombs. The bombs were dropped from very low altitude, and were hitting the ships before the bombs armed. The reporter printed the story (or told it on TV) and the Argentines promptly changed their fuzing to 2 1/2 seconds, so from then on the Argentine bombs exploded. During the war, the British lost six ships with 258 men killed and 777 wounded, mostly through the air attacks.

A perfect example of "Loose lips sink ships" !
Bruce




Pat's note: In Vietnam I heard these steel rods called "Daisy Cutters" because they made the bomb explode above ground.