Some, even on our side, claim that Amendment Two protects only the right to own non-crew-operated infantry weapons.
Were that the case, how would one implement a Letter of Marque issued by Congress under Article I Section 8 of the Constitution? That generally required an Eighteenth-century equivalent of a battleship, complete with cannon and crew.
There were also a number of privately owned forts (generally called stockades) built complete with cannons both built by and staffed by civilians.