Purpose

The purpose of this OP is to acquaint officers and necessary personnel with radio proxi-mity VT fuzes for projectiles and spin-stabilized rockets. It covers the operation, the performance characteristics, the projectiles and rockets with which used, and the theory of operation of these fuzes.

Definition

The various types of proximity or influence fuzes for gun projectiles, howitzer projectiles, mortar projectiles, rockets, bombs, and other missiles are designated by all U.S. Services as VT fuzes. The term VT has no significance or meaning as an abbreviation, but was devised for general usage in shipment orders, stock cards, loading lists, etc., when se-curity requirements during the war necessitated this.

Description

Navy VT projectile fuzes are nose fuzes, cylindrical shaped, with an ogive nose which usually follows the contour of the projectile. Their size necessitated certain changes in fuzed ammunition. The fuze cavity in the explosive filler of the projectile bad to be made much larger to accommodate VT fuzes. The base detonating fuze was eleminated from the projectile because (1) the radio proximity fuze would not perform normally in the pre-sence of tracer gases, (2) these was no need in antiaircraft fire for a base detonating fuze, (3) the absence of a base detonating fuze reduced the hazard to surface craft and shore installations from A.A. projectiles reaching the ends of their trajectories, (4) more space was left available for explosive filler. However, the VT fuzed projectiles for the 6"/47 gun do have a base detonating fuze without tracer because of their probable use in shore bombardment.

All Navy projectiles assembled with VT fuzes are stenciled on two sides (180° apart) with the letters VT, 3/4" high in black color just before the rear edge of the paint indicating the bursting charge.

Operation

VT fuzes of the U.S. Navy are of the electromagnetic type known as radio proximity fu-zes and are actuated by combined proximity and rate of approach to any target which gives a proper reflection. This includes metal objects, water, earth, etc. Operation is the same at day or night. The actual detonation of the projectile is accomplished in the fol-lowing way: A VT fuzed projectile radiates a continuous radio signal which is reflected from targets of the type mentioned. When the reflected signal from the target reaches an appropriate value, a condenser is allowed to discharge through an electrical detonator called a squib. The blast from this squib operates a standard auxiliary detonating fuze, which in turn detonates the main charge of the projectile. No setting is ncessary or pos-sible with current type of VT fuzes. They will detonate automatically if the projectile passes sufficiently close to the target.

Safety

Special effort has been given to providing safety features in VT fuzes. As a result, they are perhaps the safest fuzes in use by the U.S. Navy in regard to handling safety, safety in the bore, and freedom from muzzle bursts. VT fuzes are not immune from derangement if the projectiles are handled or loaded roughly so as to strike the fuzes on hard surfa-ces. However, dangerous conditions are improbable as a result of such treatment; rat-her, abnormal operation or duds may result.

Remarks

Because of the need for a proximity fuze and because of the effectiveness of even the early designs, the VT Fuze was placed in service before it was fully developed. The furt-her development and the information gained through service use resulted in improve-ments that were incorporated in the fuzes. This accounts for the great number of marks and mods of fuzes that have been produced and issued. As development approaches perfection, there should be fewer models and changes.