"Congress have no power to disarm the militia. Their swords, and every other terrible implement of the soldier, are the birthright of an American... The unlimited power of the sword is not in the hands of either the federal or state government, but, where I trust in God it will ever remain, in the hands of the people" (Tench Coxe, Pennsylvania Gazette, Feb. 20, 1788)
"Their swords, and every other terrible implement of the soldier, are the birthright of an American" be it a full rock and roll capable M16 assault rifle, a 105mm Howitzer, or a Saturday night special. The purpose is to be capable of killing tyrants and those who would enslave.
Edited for this post to include fully functional tanks, aircraft, & battleships.
And to note that private cannon were used in the first civil war against King George.