The start is a little weak. "It was a bright blue day" OK, but they we get the redundancy of bright blue in the water. I would start with the helicopter since that is more active.
I don't like drum to describe helicopter sounds. I've spent a number of hours in them and wouldn't use drum. Beating, as an eggbeater, is the most common, but they are loud, repetitive and metallic sounding.
What is "Recording his Admiral ship"? I was in the army, but never heard that expression,
All in all I would rewrite it to be more active and give you something on the main character to tie in to.
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Start with the Helicopter, cut the "bright blue day" line. While I have not been in a Helicopter, I have worked around them and drum does not describe what I hear. I agree the beating is the more common term, but as a result it is lacking.
I never served in the Navy, but have been researching naval customs and phrases for a WIP of mine. I am not familiar with the term "Recording his admiral ship". If it is a common Navy Phrase, most readers will be novices to that phrase (as I am).
I like where you are going with it, it just needs some tweaks.
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