There are specific procedures that must be followed to acquire a
military crash.
First you must write the agency a letter describing the wreck, with all
appropriate information, and ask if they are willing to abandon it for
salvage. You must obtain a letter from the owning agency stating that
they have abandoned the wreck.
Once you have that letter, you may proceed to retrieve the wreck.
This may not be the proper language, but is the gist of the process as
it was explained to me 25 years ago by someone who retrieved a P-51B (?)
off the slopes in Alaska and restored it. ("Moon" Spiller, Versailles Ohio)

That may have been true 25 years ago for ex Army or Air Force aircraft but some
time ago the USAF decided that any aircraft lost prior to 1962 is of no
interest to them and thus is open to salvage depending on where it lays and
whether or not it is a grave site. If it is on private property then it
becomes the property of the landowner. I recently heard of a P-51 Mustang that
was recovered with minimal damage by a landowner in 1945 and kept in his barn
until the past year or so.

The Navy however has determined that all of its equipment remains its property
forever as described by others posting here. Unfortunately the Navy cannot
seem to cooperate with people who want to help it recover historic aircraft.
Case in point, the Douglas TBD Devastator discovered over a decade ago off
Florida in relatively shallow water and amazingly intact. People who have the
coordinates of the wreck have been told that even if they recover it and
present it to the Museum of Naval Aviation they will still be sued for unlawful
recovery and the Navy will not give them permission to recover it. So a
tangible symbol of some of the greatest self sacrifice by Naval Aviation will
probably rust away to oblivion because the Navy cannot get out of its own way.

John Dupre'