A Fuze sets off explosives. A Fuse is an electrical component to limit current.

During The Battle of Britain, British Anti-Aircraft gunners were having difficulty hitting the Luftwaffe bombers. Over 1,200 rounds could be fired at one particular bomber before getting a hit.

Both the British and the Germans were attempting to solve the need for some kind of fuze that would detonate by the influence of the aircraft prior to 1939. The records indicate the continued unsuccessful work done in Germany till the end of the war.

While the concept of some kind of proximity fuze had be considered prior to World War II, the onslaught of the German war machine quickly illustrated the short comings of standard contact fuzes against modern maneuverable aircraft. Even using timed fuzes turned out to be ineffective.

In June 1940, President Franklin Roosevelt formed the National Defense Research Committee to coordinate civilian scientific research for military purposes. In September of that year, the British sent over the British Technical and Scientific (Tizard) Mission, to meet their US counterparts and share technologies already created in Great Britain (such as the cavity magnetron so critical to microwave radar). During these meetings, the British also expressed the need for other technological developments. Among these needs was a proximity fuze for anti-aircraft artillery. Such a fuze would experience as much as 20,000 Gs while spinning at speeds up to 28,000 rpm, a formidable technical challenge. The British had developed a radio circuit which could detect an aircraft, but it could not withstand being fired out of a cannon and they did not think that a circuit that could withstand these forces was possible with existing technology. At the end of the conference, research programs by the US Navy, the US Army, the Royal Navy and the British Army were tasked with developing some sort of improved AA fuze. The highest priority was given to the US Navy, followed by the Royal Navy, the US Army and then the British Army. By late 1942, a requirement for air burst for land artillery purposes was added.

Initial exploration into developing the VT (Variable Time) Fuze was done through a Carnegie funded science program, “The Carnegie Institution of Washington,” under Section T (For the leader of the section, Dr. Tuve). There was also a Section E for developing fuzes for the US Army Air Corps/US Army air Force. Since Section T sounded somewhat threatening and the device it was to develop would likely be used in war, Section T was split off as Carnegie included requirements that this science program could not be used for war purposes. As a result, Johns-Hopkins University took over the development of the fuze and formed the Applied Physics Laboratory to do so.

Their original "laboratory" was a used car lot building. There, the team of scientists, engineers, technicians and ordnance experts had to solve the following requirements:

• To design an electrical circuit that would take some sensor input, be it optical, magnetic or electromagnetic feedback, that was able to survive firing and be able to detonate close enough to bring down an airplane moving at speeds up to 350 knots.
• Circuit needed to operate in ambient temperatures ranging from -50° to 100° Fahrenheit with humidities going from 10% to 100%
• Develop a battery that would survive such conditions.
• Said battery not only had to power the electrical circuit to power the sensor, it also had to incorporate safety features to prevent accidental detonation while handling or storing the fuze.
• The fuze had to be modifiable for various American and British shells.
• The final product needed to be:
  • Able to be rapidly mass produced
  • Of high quality
  • Utilizing components outsourced to a multitude of American factories

Dr. Tuve posted the following goals:

• I don’t want any damn fool in this laboratory to save money. I only want him to save time.
• Shoot at an 80 percent job; we can’t afford perfection.
• Don’t try for an "A"; in a war "D" is necessary and enough, but an "F" is fatal.
• The best job in the world is a total failure if it is too late.
• Our moral responsibility goes all the way to the final battle use of this unit; its failure there is our failure, regardless of who is technically responsible for the causes of failure. It is our job to achieve the end result.

Initially, the US Navy’s focus was for a proximity fuze for the 5"/38 projectile. This was in hopes of improving the anti-aircraft capabilities on ships in the Pacific Theater. Dr. James Van Allen – later the discover of the radiation belts surrounding the earth – started the work of finding or creating vacuum tubes small enough to fit into the fuze cavity for a 5"/38 shell, about the size of pint milk bottle, and rugged enough to survive the firing of the shell (20,000 times the force of gravity) and endure the spin (500 revolutions per second). Remember, there was no integrated circuits, not even a transistor at this time.

By the Spring of 1941, Section T had determined that the radio (doppler radar) fuze based upon the British circuit design was the most promising of the options examined and dropped any further design and experiments with the other possibilities.

Further testing and design improvements by January 1942 saw the fuze success rate reach 52%. At this point the Navy’s Bureau of Ordnance (BuOrd) ordered the current version of the fuze into production.

Live firing tests were conducted aboard the USS Cleveland (CL-55). against drones in August 1942. There, they ran into difficulties. The squadron at NATC Patuxent River, MD had only so many drones fitted for remote control flight. USS Cleveland had already destroyed three drones with 5 shells and the squadron refused to send anymore. Prior to this test, exactly ZERO of their drones had been hit.

VT fuzed shells for the Pacific Theater were shipped out in the late Fall of 1942. The first use of the VT fuze in battle was during the Solomon Islands campaign where on January 5, 1943, the U. S. Navy light cruiser USS Helena (CL-50) scored the first combat kill using proximity-fuzed anti-aircraft ammunition, downing a Japanese Aichi D3A dive bomber south of Guadalcanal.

Admiral Arleigh Burke, U. S. Navy (Retired), former Chief of Naval Operations, spoke of their effectiveness during a 1978 interview at the Applied Physics Laboratory:

"When I went as chief of staff to [Vice] Admiral [Marc] Mitscher who commanded the Fast Carrier Task Forces, all the 5-inch/38 and 5-inch/25 ammunition was fitted with VT [proximity] fuzes and, as you well know, those fuzes knocked down enemy planes by the dozens. Had it not been for those fuzes, our ship losses and casualties in the Fast Carriers in the last half of the war would have been enormously larger. . . . That fuze was a magnificent help."

Pacific theater statistics support his statement. The proximity fuze proved three to four times more effective than conventional time fuzes, and night kill-ratios increased by 370%.

In 1943, naval guns fired a total of 36,370 antiaircraft rounds. Although only 25% used proximity fuzes, these accounted for 51% of the kills. The new shells had a lethal fragment area much larger than that of conventional fuzes—3,000 cubic feet as opposed to 60 cubic feet — a huge advantage over normal time fuzes of the day. The startling results led the Navy to increase the use of VT fuzes to 75% of the time.

The VT fuze was used as part of the shore bombardment during the Battle for Tarawa on November 20th, 1943. Two USN destroyers entered the lagoon of the atoll and began firing 5”/38 shells with an arcing trajectory. Some of these rounds were fuzed with the Mk. 32 VT fuze. Their effectiveness wasn’t known until after the 76-hour slug fest. With less than 5,000 combat effective Marines ashore halted at the sea wall, unknowingly, the VT fuzes prevented a Banzai attack which would probably have resulted in the deaths of the Marines trapped on the beach. The feared attack did not occur because of the effectiveness of the VT fuze.

The Japanese rikusentai ("Special Naval Landing Forces") in the trenches were hit hard by the VT fuzes detonating the shells in midair. Survivors were rushed to the designated hospital bunker, which was also was the headquarters bunker. The commander of the Japanese garrison, Rear Admiral Deiji Shibasaki, and his entire staff were immolated by an air-burst 5" shell upon leaving the command post/hospital in search of a secondary bunker to use as headquarters. The 2nd in command did not know of this as all the telephone line underneath the coral sand were cut in many places by shrapnel from the VT fuzed 5" shells. This prevented a coordinated banzai attack that night which saved the roughly 5,000 Marines trapped on the beach.

The 5" shells proved far more effective in supporting the Marines than all of the high velocity low angle large shells fired by the battleships and cruisers of the support force.

VT fuzes used in Great Britain were for anti-aircraft purposes and were limited to use where duds fell in to the English Channel. This way, spies in Great Britain could not recover the duds and get them to Germany. When the threat from the German V-1 “Buzz Bombs” began in June 1944, The United States lifted the ban of firing VT (POZIT – the Army code word for the VT fuze) fuzes when duds would not fall into the Channel.

The Pentagon ordered that VT fuzes not be used in Europe for fear of the Germans recovering a dud and reverse engineering it. Once in Europe, General Eisenhower had artillery battalions issued proximity fuzes but use of them for artillery bombardment was not authorized for anything but in the anti-aircraft roll. However, this order from the Pentagon was disobeyed in December 1944 during the Battle of the Bulge. Lieutenant General Patton ordered that the fuzes be used to prevent the Wehrmacht from reaching Liege.

"The new shell with the funny fuze is devastating. We caught a German battalion, which was trying to get across the Sauer River, with a battalion concentration and killed by actual count 702. I think that when all armies get this shell, we will have to devise some new method of warfare. I am glad that you all thought of it first." - General George Patton

The Germans did recover some VT fuzes that failed to detonate, but were unable to reverse engineer them before the end of the war.

By 1945, aerial bombs were also equipped with the VT or POZIT fuze. In the European Theater in April 1945, B-24s out of Italy used the fuze in the leading squadrons to silence anti-aircraft fire for the main force. In the Pacific Theater, February 1945 saw the Navy bombarding positions on Iwo Jima using VT fuzes. In the July 1945 attacks on Japan proper, a third of all bombs were equipped with the VT fuze in an effort to wipe out anti-aircraft gun crews for the follow-on bombers.

It is estimated that more than 1,000,000 people were involved in the development and manufacturing of the radar proximity fuze, yet it remained one of World War II's best kept secrets. During the production run, at total of 22,073,481 fuzes were made in the United States. Admiral Ernest J. King, CiC U.S. Fleet, stated that:

"[T]he development of the VT fuze was a major scientific achievement that has contributed greatly toward winning the war for the United Nations."

General Dwight D. Eisenhower gave a great deal of credit to the small weapon toward the end of the war:

"It seems likely that, if the German had succeeded in perfecting and using these new weapons six months earlier than he did, our invasion of Europe would have proven exceedingly difficult, perhaps impossible."

Secretary of the Navy James Forrestal put it this way:

"The proximity fuze 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."

Some consider the VT/POZIT fuze to be the beginning of smart weapons. While it could not steer itself, it had the ability to detect a target and detonate itself without any preset time delay as in the Mechanical Time (MT) fuze previously used. In its primary role for anti-aircraft use, it greatly improved many near misses into kills. As for applied science, during the entire production run, close cooperation between researchers, engineers, factories assembly lines as well as the military units utilizing the fuze was essential. Rapid feedback from the front-line forces kept development of fixes and improvements at a fast pace.

• Alexander, Joseph H., Utmost Savagery: The Three Days of Tarawa, Naval Institute Press, 1995.
  - Storm Landings: Epic Amphibious Battles in the Central Pacific, Naval Institute Press, 1997.
• APL Technical Digest, APL and the VT Fuze, APL Technical Digest, September-October 1962. Accessed February 20, 2026
• Collier, Cameron D., Midshipman 2^nd Class, U.S. Navy, Naval History, Volume 13 Number 4, (US Naval Institute August 1999.
• Conner, Roger, The Tizard Mission – 75 Years of Anglo-American Technical Alliance, Air and Space, November 17, 2015. Accessed February 21, 2026
• Ernst, Anthony, The Secret Invention: How the VT Fuse Changed World War II, FuturaFeed, December 22, 2025. Accessed February 2, 2026.
• John Hopkins University, The "VT" or Radio Proximity Fuze: Supplemental Basic Information Prepared by Applied Physics Laboratory, the Johns Hopkins University, Silver Springs MD: The Laboratory, 1945. [Released for publication on 20 Sep. 1945.]
• Robbins, Michael W., The Allies' Billion-dollar Secret: The Proximity Fuze of World War II, Military History, September 2020. Accessed February 20, 2026
• Stevens, Jonathan E., Japanese Order of Battle, 2 September 2008, Tarawa on the Web.
• Stubblebine, David, VT Radio Proximity Munitions Fuze, World War II Database. Accessed 3/27/2026.

For more information on VT fuzes, see Crosley's Secret War Effort - The Proximity Fuze.

11 April 2026 - New Essay