I agree that the Navy Vet should be able to comment on what he professes to be qualified on but I don't think the public should be allowed to carry torpedoes even with 40/80 hours of guberment training.
By the way, Guns are mounted on ships or other platforms. Weapons are carried by personnel.
At the time of the writing of the Constitution, it was understood that the 2nd Amendment protected the keeping and bearing of all military arms. People had cannon, mortars, howitzers, grenades, and armed ships. Whether the government likes it or not, people are still entitled to own any weapon they like, provided that there is no inherent extraordinary danger involved (like with CBRN weapons). At the MINIMUM, the Second Amendment protects all conventional weapons used by infantrymen, previous Supreme Court Justices have said the same, but without honoring their words.