Almost no one on the right or left can accept the 2nd Amendment in its plain wording. They (the left) deny it permits private access to arms at all or they (the right) quibble about what is included under the term “arms” or they say there can only be common sense limits or that certainly that right doesn’t extend to bad people of various definitions. No. it is absolute or is possibly subject only to the involuntary servitude provision in the Constitution. A tank may not be an “arm” but the cannon mounted in its turret most surely is.
You are correct. Note that in Article I, Section 8 (the enumerated powers of Congress) is the power to grant "Letters of Marque and Reprisal." Essentially, Congress can grant anyone the power to be a privateer (i.e. a pirate or a raider) against enemy shipping. This was actually done during the War of 1812. Raiding enemy ships required that you have cannon - MANY cannon - that you owned personally. The Founders were not stupid men, they understood this VERY well. Thus, logic and the language of the Constitution indicated that cannon are protected arms.
I would also make the argument that ALL arms capable of being carried/used by a single person or even a 2- or 3-man team are protected under the 2nd. Our side employed rifles in the Revolutionary War, and at the time rifles were fairly high-tech, certainly higher tech than the Brown Bess muskets of the British. So we have the right to keep and bear ANY firearm now, since that right obviously existed back then.