Vlad, was there some info on that Rocket?
This is a Tiny Tim rocket en.wikipedia.org/wiki/Tiny_Tim_%28rocket%29. It is a plane launched HE rocket designed specifically for attacks on Japanese reverse slope military fortifications on Okinawa. The regular artillery had problems hitting the “other” side of a mountain.
That VT fuze looks to be a MK 32, one of the early ones. It, and others like it, are what made the 3’’/50 Rapid Fire guns effective. Without it, the old 3" (and 5") AA guns were nothing more than “spray and pray” ammunition eaters.