[RedMonqey]

I say after 200 years, its "finder's keeper's rule kicks in.

[Redbob]

You're right, of course, but "finder's keepers" pretty much depends on whose backyard you're playing in...

[GladesGuru]

Military vessels and equipment remain the property of the nation - probably forever.

German tanks found in a Scandinavian river were claimed by Germany. They kept the best. The rest, though scoured to shreds by decades of moving water and grit, were snapped up by collectors.