Instapundit pointed me to this post, where Mark Kleiman argues that there is Constitutional protection for a long gun, owing to what I would call a militia utility test. If one can demonstrate what the militia is for, and how it should be armed, the Constitution protects the right to own that kind of arm---but none other. He then turns that argument to sidearms.
"A side-arm is not a weapon of war, because it lacks the range to strike the enemy. No private soldier carries one. Side-arms are for officers, to threaten, or if need be to shoot, disobedient subordinates. The rank-and-file carry long guns."This is true for the Russian model, and others, but not for the present American one.
Sidearms are indispensable for searches of or working in such places as buildings, tunnels, and vessels, for driving vehicles, or for those carrying specialized equipment where weight of one's kit is at a premium. All of these are conceivable roles for members of various teams in a well-regulated militia.
I carried a sidearm, as a mid-level enlisted man, just last year in Central Asia. It was there in those cases when I could not carry a rifle; each time, I had an escort with a rifle nearby. I was issued both pistol and rifle, and I was free to choose which to bear according to the situation.
Anyone who carries a crew-served weapon, such as an MG, rocket launcher, in fact anything other than the standard service rifle, carries a sidearm as the backup in case the primary arm fails or its ammunition is exhausted. Private soldiers tend to acquire sidearms whenever they can; if they are not issued sidearms at the outset it is more likely a budgetary or training decision rather than one of philosophy of how men should be armed.
"A militia member fights as a soldier, with whatever arms are conventional at the time . . . "Even soldiers fight less like soldiers today, as there are fewer and fewer of them, and more specialists in support and services fields, enhancing the effectiveness of the fewer but better-equipped and better-supported infantrymen. The tooth-to-tail ratio of the modern army is diminishing (whether this is sound theory, or effective in practice, is outside our scope here); we can expect the same for the militia if they are to be easily assimilated into the army, especially in a culture that prizes diverse experience, advanced education, initiative, and individualism. If our militia reflects our society and its values, we will not be forming waves of conscripts prodded forward by pistol-waving officers.
Organizationally, they'll look more like investment clubs, HAM radio clubs, and fantasy-football leagues. (I expect ridicule out of this last point, and perhaps I deserve it. So horse-laugh now and get it over with.)
Historically, the sidearm was developed for cavalry, because the service rifle (or its equivalent of that period) was too cumbersome for operation from horseback. The Confederate Colonel John Singleton Mosby was the first cavalry officer to order all of his troops to abandon the saber completely and standardize on the revolver among his troops.
The M1 Carbine of World War II was conceived, among other reasons, as a means to eliminate the several other classes of small arm, including the sidearm, so that the US would need to supply only the Carbine and the M1 service rifle. Obviously the sidearm continues to this day, because there was, and is, still a valid and fairly common need for it. Uncle doesn't issue M1 Carbines any more.
So I disagree that the sidearm would not enjoy strict Constitutional protection under the militia-utility standard. It is neither an officers-only nor a specialist's weapon. It is a tool designed for certain applications, and a militia could be called upon to carry out those applications. The same can be said for the shotgun and the SMG; Jeff Cooper's essay "The Role of the Five" explains this, and if I can find it online I will link it here later. They have their uses in a militia organization, especially one formed as American values and character would have it. The full-dress service rifle should be considered its principal arm, necessary but not sufficient.