WHAT DOES UNDERWATER NUCLEAR TEST 'UMBRELLA' MEAN?

With test moratoriums to the horizon, American weapons labs rushed out several new types. A hard deadline for testing was set at midnight (0000 hrs), 31 Oct 1958, as negotiations have been set to start that day, and the program shows it, with 29 tests executed in Oct, four of them on the final working day. One other test was cancelled due to the fa