WWII you could buy surplus P-51s
without the 50 cal machine guns and bombs, it was just an airplane, not a weapon. Further, owning an airplane comes with a huge book of restrictions (even in 1946). There is nothing about owning and flying an airplane that remotely resembles "shall not be infringed".
My point is that the founders did not consider privately owned warships to be protected by the 2nd. So obviously they envisioned a line of separation... musket yes, warship no.