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.
It was fun after you got over the sheer terror of what you were about to have to do. We were also trained on the Helicopter Emergency Escape Device (HEED) which is like a miniature scuba tank you carry on your vest. It has 5 minutes of air. Fortunately I never had to use it for real.