What was the most advenced fuse during World War 2?

Answer 1

The proximity fuse. This was a tiny radar set fitted into the nose of the artillery shell. Very useful against aircraft. With the proximity fuse it was no longer necessary to score a direct hit, or set the fuse to detonate the shell just as it was passing near the enemy aircraft, which was almost impossible to do and was a matter of pure luck. With these new, super-secret fuses all the shell had to do was pass near the enemy plane and the fuse would detonate it when close enough to cause fatal damage. These highly secret shells were only used by the US Navy for most of the war, and were only fired over deep, open water, never over land, to avoid the possibility that an unexploded one might fall into enemy hands.