Proximity Fuze - What does "VT" Mean?

by Tony DiGiulian
Updated 21 April 2009

Every so often, someone writes me to say that they believe that my definition for "VT" as being for "Variable Time" is wrong because the famous Ian Hogg in his 1978 book "British and American Artillery of World War Two" gives a different definition.  In this book, Mr. Hogg insists that the term "VT" was coined simply because Section "V" of the Bureau of Ordnance was in charge of the program and they allocated it the code-letter "T".  None of my correspondents seem to note that no serious work on the subject prior to or since that time agrees with Mr. Hogg.  Instead, all other independent works state that "Variable Time" is the correct definition for VT.  See, for example, Norman Friedman's "US Naval Weapons" of 1983 or John Campbell's "Naval Weapons of World War Two" of 1985.

This non-support of Mr. Hogg should not be surprising, as the truth of the matter has been established since shortly after World War II when the official "U.S. Navy Bureau of Ordnance in World War II" by Lt.Cmdr. Buford Rowland and Lt. William B. Boyd was published by the Department of the Navy in 1953.  Rather than paraphrasing, I will quote the relevant paragraph in full from page 279 of this work:

'This type [of proximity fuze] was finally selected as the most promising for antiaircraft use.  It ultimately received the name VT, or variable time, for no particular reason except that some designation was necessary and Capt. S. R. Shumaker, Director of the Bureau's Research and Development Division [NDRC], hit on the term as one that indicated the special nature of the fuze without violating the strict secrecy surrounding its operation.  In completed form, the VT fuze consisted of four principal parts:  A radio frequency oscillator and receiver, an amplifier and thyratron tubes, a battery, and an explosive train incorporating vital safety features.'
Seems fairly straightforward enough, but if not satisfactory, then let's look to see what Dr. Ralph B. Baldwin, one of the designers of the fuze and who was in on its development almost from the very beginning, has to say in his definitive work, "The Deadly Fuze - Secret Weapon of World War II" (1980, Presido Press, ISBN 0-98141-087-2) on page 9 of his book:
'Since the words "radio proximity" and "influence" were classified in relation to this fuze, other code terms were adopted by the American and British services.  The British adopted the term "V.T.," meaning "variable time," as suggested by Capt. S. R. Shumaker in a conversation with Cmdr. A. M. Hutchison, RN, of the British Admiralty delegation.  In the summer of 1943, the American Joint Chiefs of Staff adopted the use of this term, emphasizing that it was only a designation and had no meaning in itself.  The United States Army referred to the fuze by its own code term, "pozit" fuze, which was first suggested by Capt. Jean P. Teas.'
Elsewhere in this book, Dr. Baldwin notes that the fuze was always called "proximity" or "influence" before the VT designation was adopted, it was never called "The Section T fuze" or any other variation of that sort of name.

So, both the official history of BuOrd and the definitive first-person story by one of the fuze designers both clearly state that "VT" stood for "Variable Time."

It should also be noted that in May 1942, Section T was divorced from the NDRC and was placed directly under the Office of Scientific Research and Development (OSRD), becoming "Section T, OSRD."  At this same time Section T also was moved from the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, which did not have adequate facilities for such an expansion, and was set up in a new laboratory in Silver Spring, Maryland, under The Johns Hopkins University which took a contract with the OSRD to carry the proximity fuze work.  This laboratory was designated as the "Applied Physics Laboratory of The Johns Hopkins University," usually abbreviated as APL.  So, any use of the "Section T" name in regards to proximity fuzes after this time should be treated as suspect as most of the direct work on these fuzes was under the auspices of APL and not Section T.

One last point:  Some may question where Capt. Shumaker came up with his designation.  The following is pure speculation on my part, but it seems a rather simple deduction.  The fuzes used by the USN for AP rounds were originally designated as "VD" standing for "Variable Delay" since the time that the first ones were introduced prior to World War I up until the 1930s.  Next, as many readers are aware, the fuzes for USN AAC rounds that used a timer in them to determine when the round burst were designated as "MT" which stood for "Mechanical Time."  Thus, Capt. Shumaker, who would have known both designations as a BuOrd officer, appears to have simply combined the first name and letter of the VD designation and the last name and letter of the MT fuze in order to come up with his new "Variable Time" or VT designation.


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