Hello Rising Sun*.
I rewatched the films now and i saw what i thought about - i think the dokumentation out of which the second video you posted above is, seems to be somehow ‘too humanistic’.
If you rewatch the first video and take a closer look at the time 2:50 to 3:05, you will see the same sequence as in the second video!
Now the ‘grenade’ footage seems pretty similar in the context with the other material shown in the first video [same quality, colours and probably the same submarine? etc.], so it probably belongs to the same film.
I don’t know what caused the explosion in the water [i don’t think they would blow ‘something’ [in general]up that near to their boat]. The second impact [the rifle projectile] was most definately shot as a reaction to the explosion.
So seeing that the naval personal shot those guys in the water i wonder what weapon caused the explosion - was it really a grenade? If yes - just a macabre, but possible, theory - did US submarines have handgrenades on board?
Good evening.