Early 'Smart Bombs' at Bell Labs
Home ] Up ]


Early 'Smart Bombs' At Bell Labs

 By A. C. Dickieson
Reprinted from Vintage Electrics Volume 3 #1

In June of 1940, at the fall of France, President Roosevelt declared an "unlimited emergency". What those words meant to Bell Labs was that we turned almost all of our resources to work for the military. As might be expected, this brought on a great variety of projects- communication, radar, research, gun control, submarine detection, on and on.

As 1941 wore along, the German submarines were taking a serious toll of allied shipping. From April through December 1941, they averaged 175,000 tons sunk each month, and the rate was Increasing. Many of the Allied counter-measures involved air plane attack on subs on the surface. Under water, they used storage batteries for propulsion. These batteries had to be recharged while the sub was on the surface.

Our planes would detect such subs by radar and speed over. But the sub would detect them by radar also, and submerge. By the time the plane arrived, its usual weapons were useless. Clearly, a weapon was needed that would chase and catch them under water. Some very promising experiments were performed at the Harvard Underwater Sound Laboratory, looking toward a small, acoustically steered torpedo that could be dropped from an airplane, to chase the sub by steering on the sound from its propeller. Our research people, especially John Steinberg, were involved because of their pioneering work on measurement of the transmission of sound in the undersea environment.

In December 1941, Bell Lab was engaged to design the torpedo, to be manufactured by Western Electric. Great secrecy and the earliest possible schedule were stressed. My group was assigned the design of the electronic system. This was a small part of the overall. The project manager was Charles Weibusch, who did a great job of steering the design of the body, propulsion gear, steering, hydrophones, etc.

The design was completed by October 1942, and production started to roll in quantity, in March of 1943. It was deployed to the fleet immediately, with great haste and secrecy. Named the Mark 24 Nine, it was an important factor in breaking the back of the submarine attack. 37 U-boats were sunk, and 18 seriously damaged by the Mark 24. The secrecy was so effective that the Germans did not know until the end of the war what had happened.

From the electrical design standpoint, the electronic system was not too complicated. There were two hydrophones on the left and right sides of the body, and two top and bottom. Signals from the side hydrophones were compared. If one was larger than the other, the left-right rudder was turned in the direction to equalize. The same went for the up-down rudder. The combination pointed the torpedo toward the sound. Several hundred pounds of TNT did the damage on contact.

The challenge was that all this took 21 vacuum tubes - no transistors in those days. No one had ever dropped a vacuum tube system into the water at 300 knots before, and expected it to work! We mounted the equipment on a round panel (to fit into the body), with the long dimension of the tubes and other gear facing the nose. On impact, this panel flexed, and took a permanent set of about 1/2 Inch. The layout allowed for this motion, without crushing parts together.

We were happily surprised to find that vacuum tubes were strong and withstood this kind of impact very well. But there was another complication: these were tubes out of ordinary radio sets, that took 30-60 seconds for the heater to warm up to operating temperature. We only had 6-10 seconds from the airplane drop to the time when it had to be operating in the water.

Our solution was to put double voltage on the heaters when we dropped, and cut it back to normal under control of a depth controlled switch. The vacuum tube designers were aghast at such a notion. On test though, most of the tubes took this well. Some would burn out immediately. The wires from the outside went through a glass press to reach the inside. We found that in some cases, a little bit of the wire would not be covered by glass, and there was local overheating.

Our manufacturing people designed a fixture like a great hammer and anvil. A complement of tubes was mounted on the hammer (as they would be in the torpedo), double voltage was applied, and the hammer banged down on the anvil. The tubes that survived this test were used. We tried, but never really knew how many Gs of impact were developed, but it was one hell of a bang! We never had a report of failure that could be ascribed to vacuum tubes.

Our whole team understood the urgency of this project. Ships were being sunk faster than we could build them, to say nothing of their contents. We worked seven days a week for four months to get the design completed, and our manufacturing people did the same when it was their turn. We found real satisfaction in making a contribution, but our medical people were pleased when we slackened off some. This was one of the first "smart bombs".

Everyday we rescue items you see on these pages!
What do you have hiding in a closet or garage?
What could you add to the museum displays or the library?



DONATE! Click the Button Below!

Thank you very much!


Material SMECC 2007 or by other owners 

Contact Information for
Southwest Museum of Engineering,
Communications and Computation 

Talk to us!
Let us know what needs preserving!


Postal address 
smecc.org - Admin. 
Coury House / SMECC 
5802 W. Palmaire Ave 
Glendale, AZ 85301 

Electronic mail 
General Information: info@smecc.org