This is very good, I like good descriptive writing and the 'odd' touches you bring in about training, fatigues and flotation devices to what seems to be a story about someone messing about in the water kept me reading it until it became clear. I imagine that dropping into the sea after a crash would feel a little rushed and frantic...I think there are times to rush a scene along and times to keep the pace slow and measured. I agree with Antiochus III about the sudden shift to a rather explanatory nature in some bits, but firstly Tom Clancy gets away with this all the time and secondly, let's wait until I post a short story before I get to knock yours...!
Keep writing stuff and posting it. I'm writing a short excerpt about a French rascal and layabout who gets 'persuaded' to join the First Crusade and probably ends up being a serious dirty tricks man...this has inspired me and I shall post some of Jules' nefarious adventures soon, I think.
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