Not exactly and if you were to pick one and only one feature to be THE main feature, automatic fire of a rifle round that can be shouldered by any GI would be the requirement. Ultimately, there are several main features of an “assault rifle” (intending to use the term correctly in this context; as compared to a “battle rifle” or a “submachine gun.”)
The reason there are multiple main features to an assault rifle has to do with its requirements. An assault rifle needs to perform all squad roles in an assault on a fixed position. The tactical advantages which are presented by such a weapon are numerous. Keep in mind that modern squad tactics in an assault on a fixed position were being figured out real time on the fly during World War II. The strategists had to make their most intelligent guess as to what the next war would look like and they are never completely right.
Let’s pretend we are in very late war Western Allies and we are going to PLAN an assault on a position. What do we need?
• several riflemen with M1 Garands to provide base fire to targets outside carbine range
• several riflemen with M1 Carbines for maneuvering fire to escort the dedicated assault team
• at least one BAR man to provide mass suppression for the main assault thrust
• an assault team armed with submachine guns and shotguns for spraying and praying when inside the target
Logistical nightmare:
-your assault team gets mopped? Fallback unless you’ve got more smgs waiting to try a round 2.
-Your carbiner gets hit on the assault escort? Your assaulter is likely to get pinned down and need a rescue. At the very least, you’ll need to get him some additional escorts
-Have you thought about ammo? Magazines? The carbine takes .30 CAR in its own magazines. The BAR takes .30-06 in its own magazines. The M1 Garand takes .30-06 in an en bloc clip but at least the magazine can be loaded one round at a time from the open bolt position. Tommy guns fired .45ACP. M3s fired .45ACP. 1911 sidearms fired .45 ACP but it was unusual for any soldier but an officer to carry a sidearm. Are you out of .45? Tommy gun is fucked. Out of .30 CAR? Carbiner is fucked. You’d better pray to God you aren’t in such a desperate situation you’re out of .30-06 but that’s probably a bridge too far. The only things that are interchangeable about this situation are that the Tommy can fire sidearm ammunition and a BAR magazine can be loaded with standard issue .30-06 from any rifleman.
So…enter the assault rifle.
YES, it has an intermediate cartridge because the M1 Garand was designed to provide enough punch to a horse at 500 yards to stop a cavalry charge. That’s an obsolete feature. …45 Auto Colt is purely a pistol round and is only effective in an assault by rapidly deploying multiple projectiles into the enemy’s chest. The .30 Carbine is punchier but not stout enough to maintain killing power at the fringe of combat range. Something with better stopping power than .30car but without the recoil of .30-06 was demanded.
An assault rifle needs to operate its own action (automatic fire obviously requires this, but it is worth identifying separately because it was an Ordnance requirement during the “Light Weight Rifle” era that ultimately transformed into the
An assault rifle also must support automatic fire mode for cqb. When an enemy is inches to feet away from you, it’s not good enough to get a kill shot; you need to issue lights out so that his trigger finger doesn’t work on his way to the dirt. 3 to the chest with one pull does it
needs to be light enough and short enough to use while maneuvering an approach or in a building. The reason the carbines were used for this role in WW2 was that the shorter body of the rifle compared to the Garand made it much more practical for the task. The lesser weight made it easier to carry at a full sprint under fire. The lower recoil made it easier to fire effectively while on the move. An assault rifle has to perform at least as well in these tasks
Blah blah blah other things too, but those are the majors