What wimps. When I went through helicopter dunker training, we had no knives and did it blindfolded three times! No $hit, Miramar NAS, 1988.
I didn’t get the chance in the big dunker however, (the one that simulated a big helicopter like a Chinook or Sea Knight) but my buddies who did told me that was a fun experience! Nothing like getting a boot in the face as you and a bunch of other guys all try to get out after being blindfolded, submerged, and inverted.