After 70 years at the bottom of a lake, I doubt those .30 cal guns are operable or even recognizable to the average person.
RIP to those young airmen.
Some of the stuff they discover in lakes and bogs in Europe will clean up and be not only well-preserved, but fully functional without too much effort. Governments - ours not excepted - generally get quite hysterical about newly-discovered a/c armament and take it into immediate state custody. As the years pass, some entities have become more amenable to preservation than scrapping; occasionally, they allow a bit more. ( http://www.youtube.com/watch?v=0PjLpqWFFEo )
Mr. niteowl77