VT.

This is coolbert:

VT = Variable Time. Variable time fuze. Victor Tango.

Here with some You Tube video, the VT fuze. Rated third most important Research and Development [R and D] project of the Second World War [WW2]. Third only behind the Manhattan Project # 1 and the B-29 bomber # 2.

Over sixty companies and research labs [three score as described] in the R and D process. Reputedly over two thousand companies involved to some degree in the manufacture of the VT fuze itself.

"fuze : a mechanical or electrical detonating device for setting off the bursting charge of a projectile, bomb, or torpedo"

VT described as a radio transmitter and receiver in a tiny package used to fuze an artillery round. Proximity to an object allowing for detonation without impact on the target. Radar as understood. Radio Direction and Ranging [RADAR].

As explained and thanks to You Tube.

In the modern context VT fuze as arming the warhead of a surface-air-missile missile, detonation releasing hundreds "of high-energy objects". Actual missile hitting the target not required for a shoot-down.

Anti-aircraft-artillery [AAA] rounds using VT fuze SIX times for effective. Perhaps even more effective when used by ground force tube artillery and directed against enemy troops in the open or even in dug in positions without overhead cover. That downward trajectory spew of shell fragments most deadly.

coolbert.