Jan 5

Variable Time Fuse’s Combat Debut

Wednesday, January 5, 2011 12:01 AM


On 5 January 1943, Task Group 67.2, commanded by Rear Admiral Mahlon S. Tisdale, carried out a bombardment against airfields and military installations at Munda, on the Japanese-occupied island of New Georgia in the Solomons. Shortly after the remainder of Task Force 67 joined up with Tisdale’s warships, Japanese aircraft launched attacks on the force—air strikes that resulted in the near miss of the light cruiser USS Honolulu (CL 48) and the damaging of the New Zealand light cruiser HMNZS Achilles. During this action the light cruiser USS Helena (CL 50) became the first U.S. Navy warship to employ the new Variable Time (VT) or proximity-fused antiaircraft shells to defend the ship against the attacking planes. Her VT-armed 5-inch/38 guns succeeded in downing a Japanese Aichi Type 99 VAL carrier bomber in the fight.

The then highly secret VT shell relied on a radar fuse located in its nose to give off radio waves that bounced off the incoming plane, and when the shell came within a lethal distance of the aircraft it automatically exploded—knocking its target out of the sky. Although it was used by U.S. Navy combatants in the Pacific in the months that followed, this wonder weapon achieved its greatest role some two and half years later, in the waters off Okinawa, Japan. There, during the lengthy fighting to seize that pivotal island, proximity-fused antiaircraft shells from the quad 40mm and 5-inch/38 guns of destroyer escorts, destroyers, cruisers, and battleships in the Fleet shot down hundreds of Japanese Kamikaze aircraft whose pilots were bent on hitting the American ships offshore by crashing into them. By downing these suicide planes before they could hit their targets, the VT-fused shells saved the lives of thousands of Allied sailors who otherwise would have been killed.

  • Thomas Wildenberg

    Although the VT fuse was a significant technological achievement, its role in defeating the Kamikaze threat has been grossly exaggerated. According to official U.S. Navy records, approximately 80% of all Kamikazes shot down by shipboard AA fire were brought down by automatic weapons (40mm and 20mm). Most of the remainder were brought down by 5-inch gunfire using both common and VT fused projectiles in ratio of about 9 to 7. Only 17 of the 245 Kamikazes shot down by shipboard AA fire during the campaign in the Philippines were attributed to the VT fuse as reported by the Antiaircraft Operations Research Group, Headquarters of the Commander-in-Chief, United States Fleet, Study No. 4, 1 June 1945. The VT fuse could not be used effectively against the Kamikaze because of inherent deficiencies in the Mk 33 and Mk 37 directors, which were unable to handle the high speed diving tactics employed by most of the suicide attackers.

  • Rebecca Bertok

    I am a self educated World War II historian. My interest in the VT fuse is personal. My father was aboard a cargo ship struck by a Kamikaze off Okinawa. Reading Matome Ugaki’s Fading Victory and G.M. Giangreco’s Hell to Pay led me to an NHC report and diagram about VT fuse development. In essence that type of shell was not the normal load and the decision to use it required a command to the turret (if one could be made in time). I think in this matter I am concurring with Mr. Wildenberg. Do I smell a book in there, Sir? I have gained from your others,except for the most recent on torpedoes

  • Rebecca Bertok

    Corrections and Brief Continuation of the above post: there was initial USN concern over the supply of VT shells that could be produced. Apparently, by Okinawa the supply was adequate. Another twist in the shipboard defense battle was that as the Japanese began to run out of traditional Kamikaze aircraft, they resorted to older, wooden models (trainers, biplanes, etc.). The wooden construction made the VT fuse non-responsive. D. M. Giagreco observes wryly that these may have been the first “stealth” aircraft.
    Finally, Robert C. Stern’s recent describes Project Cadillac (named for a naval radar facility in Maine). The Project’s goal was to develop an airborne early warning system stuffed into a TBM airframe with two aircrew The craft was designated XTBM-3W and flew in 1944. It was designed to project radar down to a ship’s CIC. Benefits included greater response time and a bird’s eye view versus a surface one.
    Of course S. E. Morison includes some commentary on the VT fuse and references controversy in Volume 14 of his classic series.
    I expect the torpedo book will be an excellent read!

  • Mr Sperry

    I have what seems to be some type of warhead tip. it has been in my posesion for about 8 years or so.
    I found it in my old barn. Me being of curious nature, I dismantled it a little and then I realized what I had laid out in pieces right in front of me. I really thought it was part of a ships compass or something at first. But when I had seen the pin switch on top, under a small aluminum dome, I was sure it was part of a warhead. I would like to know where to take something to be defused or to make non-leathal.
    Just to know what it is off of would be great too.
    If you have any info, I would greatly appreciate it.
    Thank You
    Mr Sperry