During and after the American revolution, there were individual Americans who were able to salvage cannon from downed British and American warships.
These cannon were WMD's in the 1770's.
No one seized them. They were allowed to keep them.
From http://www.alankeyesblog.com/
[Keyes] On the Second Amendment
The Second Amendment right to keep and bear arms is in jeopardy these days--dangerously so. The purpose of the Second Amendment is to ensure that we will remain an armed people, able to defend our liberty.
In our defense of firearm rights, we must emphasize this fundamental purpose of the amendment. If we leave the impression that we think that the right to keep and bear arms concerns hunting and sports shooting, and making sure Americans have the right to entertain themselves with guns, we will actually contribute to the false view that the Second Amendment is an historical curiosity, hardly deserving the effort it would take to officially remove it from the Constitution.
The right to keep and bear arms derives from our duty to retain the basic means necessary to defend our country and our liberty. Certainly it is true that the actual defense of our national borders is normally delegated to the professional military. But we must never think that this revocable delegation of responsibility for national defense is a transfer of ultimate responsibility. We, the people, are responsible for the defense of country and liberty, and the Second Amendment is crucial to our performance of that duty