The Proximity Fuse

SHELLS (13 K)
A variety of artillery shells with proximity fuses.
all photos courtesy Crosley Corporation
   Three critical secret projects were pivotal for the Allied victory in World War II. Two of these were the development of the atomic bomb and radar. The third was the development of the proximity, or VT (Variable Time), fuse.

   Prior to the war two types of fuses were used: the timed fuse was set to explode at a predetermined time after firing, and the contact fuse, used in smaller caliber weapons, exploded on contact with an object. Neither was effective against the highly maneuverable airplanes that had been developed since the end of the First World War. The British began the development of a projectile which would automatically detonate in close proximity to the target in 1939 and the American effort began in early 1940.

   The U.S. Navy was particularly concerned with the vulnerability of surface ships to aircraft attack. It was clear that the problem of fleet protection demanded a drastically more effective means of destroying enemy air power than either the timed or contact fuse provided.    Section T of the Applied Physics Laboratory at The Johns Hopkins University, under the direction of Dr. Merle A. Tuve, was assigned the task of developing and overseeing the production of a proximity type of fuse for the Navy's 5-inch guns, which were their primary long-range antiaircraft weapon. The theory was simplicity itself: the fuse would contain a miniature radio transmitter-receiver which would send out a signal. When the signal reflected back from the target reached a certain frequency, caused by the proximity of the target, a circuit in the fuse closed firing a small charge in the base of the fuse that detonate the projectile.

   The theory may have been simple, but the problems encountered in all steps of development and after the fuse was released for use by the fleet were formidable. Consider that the components in the fuse, including tiny glass vacuum tubes, had to withstand the shock of being fired from a 5-inch gun. This set-back force of 20,000 g's is instantly generated by accelerating the projectile to a 2,800-foot-per-second muzzle velocity. In addition, the shell's brief trip through the gun's rifling grooves starts it spinning at 25,000 revolutions per minute. Safety features had to be built in to protect the men handling the ammunition in transit and aboard ship. Additional safety features were necessary to prevent the shell from exploding too soon after firing which would endanger the gun crews and nearby ships. A self-destruct feature was also necessary to prevent dud fuses from falling into the hands of the enemy. Moisture was an ongoing problem that had to be dealt with and there were many other problems that are too numerous to mention here.

   The Crosley Corporation of Cincinnati, Ohio, was one of five companies that assembled proximity fuses. A total of 87 different firms using 110 factories were engaged in some phase of production work. Crosley's involvement began in late October 1941 when they were contacted by the Bureau of Ordnance and told that they would be contacted later that month concerning a "top secret, top priority" project. Lewis M. Clement, Crosley's vice-president in charge of engineering, recalled that Crosley had been selected because they had the required background in electrical and mechanical engineering and in mass production. The letter of intent from the Navy came in late November 1941 and a contract for 500 fuses in December. The first accepted fuses came from the production line in September 1942. On January 5,1943 Lt. "Red" Cochrane, commanding the aft 5-inch battery on the light cruiser Helena, shot down a Japanese Val dive-bomber with the second of three salvos of VT-fused shells, near Guadalcanal. The fuses were manufactured by the Crosley Corporation and this was the first kill of enemy aircraft.

   Although primarily a supplier to the Navy for use in the Pacific and the Mediterranean theaters, Crosley fuses were used with great success by the British against the V-1 buzz bomb, by the U.S. Army on the European continent in the defense of Antwerp against V-1 attacks, and in the Battle of the Bulge.

   In a post-war interview, Lewis Crosley said that fuse production reached 16,500 units per day. The Crosley Corporation employed ten thousand people and worked around the clock, seven days a week. Mr. Crosley said, "We enlarged until . . . we were the largest employer and produced more than anybody in Cincinnati, including any of the other big companies located in Cincinnati at that time. We had some very, very secret and wonderful products that we produced in volume for the Armed Forces and we got a lot of credit for doing it." Bureau of Ordnance figures show that Crosley produced 5,205,913, or 24%, of the slightly more than 22 million proximity fuses manufactured during the war.

   The importance of the proximity fuse to the successful outcome of the Second World War is best stated by those who witnessed it's effectiveness.

   James V. Forrestal, Secretary of the Navy said, "The proximity fuse has helped blaze the trail to Japan. Without the protection this ingenious device has given the surface ships of the Fleet, our westward push could not have been so swift and the cost in men and ships would have been immeasurably greater."

   Prime Minister, Winston S. Churchill was quoted as saying "These so-called proximity fuses, made in the United States ... , proved potent against the small unmanned aircraft (V-1) with which we were assailed in 1944."

   Finally, Commanding General of the Third Army, George S. Patton, said, "The funny fuse won the Battle of the Bulge for us. I think that when all armies get this shell we will have to devise some new method of warfare."

MARK 53 PROXIMITY FUSE (61 K)

PROXIMITY FUSE (38 K)