Seventy Years Ago: VT Projectiles Shoot Down Japanese Dive Bomber

January 5, 1943. Task Group 67.2 (Rear Admiral Walden L. Ainsworth) bombards a Japanese airfield and installations at Munda, New Georgia, Solomons Islands. After the rest of Task Force 67 joins TG 67.2, Japanese planes attack the force, just missing light cruiser Honolulu (CL 48) and damaging New Zealand light cruiser HMNZS Achilles, 18 miles south of Cape Hunter, Guadalcanal. In the action, light cruiser Helena (CL 50) becomes the first U.S. Navy ship to use 5 inch/38 caliber Mk. 32 proximity-fuzed projectiles in combat, downing a Japanese Aichi Type 99 carrier bomber (VAL) with her second salvo

This was a major technological triumph. These 5-inch projectiles contained a tiny radio proximity device, essentially a miniature radar, which caused the projectile to explode if it came close enough to the airplane to do damage. This system, under development since mid-1940, was a vast improvement over the mechanical time fuze previously used against aircraft. It also replaced contact fuzes that had to actually hit the aircraft to explode.

To conceal the purpose of the projectiles, they were designated as "VT-Fuzed projectiles" (Variable-Time fuze).

The story of development of the proximity fuze is detailed here in an article on the Naval Historical Center web site.

The greatest challenge was to ruggedize the miniature electronic tubes used in the circuitry back in the day before transistors.

Mark 53 Proximity Fuze