TimActual had a comment on the Marine air assault on Hawaii:
I have never understood why the Marines like to use BIG targets to carry troops.
And that air assault looked pretty casual to me. We were always taught to get everything off the LZ ASAP, birds and men.
As to why the Marines tend to choose somewhat larger helicopters than the Army, I alluded to that years ago in a post on the Chinook.
The Army, as it evolved its air assault doctrine, saw infantry troops (as part of a combined arms team with artillery and aerial fire support) delivered directly upon the objective. One key doctrinal issue that wanted to address was unit integrity. They wanted to ensure that the basic unit, the rifle squad, was delivered intact. That meant the optimal assault helicopter would carry an 11 man rifle squad, which, from the UH-1D on through to today’s UH-60M, is just what seating is provided, if not always the actual lifting capacity. Between three rifle squads, a weapons squad, and the platoon headquarters, four helicopters could lift a single assault platoon.
The Marines, while they might have liked to embrace the same philosophy, faced two challenges the Army did not. First, they were far more constrained in terms of manpower. Unlike the Army, with the majority of its aviators being warrant officers, the Marines aviators are all commissioned officers. Given that the total number of commissioned officers available to the Marines was set by Congress, they couldn’t afford as many helicopter pilots as the Army, especially considering the numbers needed to fly the Marines fixed wing aircraft.
The other, bigger issue was simply one of space. The Marines are a seagoing force. That means they have to be embarked on ships, and even the largest of ships for amphibious operations have severe constraints on the total numbers of aircraft they can operate.
The carrying capacity, both in weight and in volume, increase faster than the actual size of an aircraft. That is, an aircraft twice as large as another can reasonably be expected to carry not twice as much, but three times as much. It didn’t take long for the Marines to realize that two CH-46s, carrying 25 troops each –that is, a Marine rifle platoon- took up a lot less deck space than the 4 or 5 UH-1s it would take to lift a platoon. As an added bonus, it would take only half as many pilots, not to mention the numbers of enlisted aircrew, and maintenance personnel.
The Marines did understand the risk involved, namely that losing one aircraft had a much greater impact, particularly in terms of lives potentially lost, and also in terms of unit integrity. If a platoon loses a squad, it might theoretically still be able to function. But losing half a platoon most certainly renders it combat ineffective.
That same size issue, known as the spot factor, also influenced the size of the MV-22B, which accomodates 24 troops, in a spot factor little bigger than a CH-46. In that case, you’re trading an increase in size for an increase in performance, rather than capacity. It’s a tradeoff.
As to TimActual’s comment on using the CH-53E itself, that’s also somewhat influenced by the confines of amphibious shipping. The MV-22 is fine for landing the initial waves. But there are only so many available aboard a ship. And the embarked Marines simply must have a certain number of the larger CH-53s aboard to move things like artillery. But they aren’t always doing that, so they are occasionally available for the lift of troops.
As to expeditiously moving off the Landing Zone, it should be remembered that Marine doctrine (and really, Army as well) is to conduct the landings away from known enemy positions. The aerial movement is simply the first stage of maneuver, leading to the dismounted movement to either a defensive position, or the line of departure for the assault. One should not dally on the ground, or disembarking the helos, but neither is tripping off the back ramp a good idea because one was unduly rushing.