France paratrooper can also simulate commandos along european shore.
Also, you can identify special infantry or Marines with a Control Marker below the sculp.
That way, you can increase their cost without having to buy 1914 or 1941 to get different Infantry sculpt.
I still wonder if a 3 IPCs unit can be a balanced cost for a weaker Marines unit able to move with Cruiser and BB.
As written elsewhere:
Marines as simply Marines and nothing more
Sea movement bonus:
1 Marines unit can be carried on 1 Battleship or 1 Cruiser.
Transport can load 2 Marines or 1 Marines plus any other 1 ground unit.
Gets +1A on amphibious assault only.
No combined arms with Artillery.
No production limit number.
That way, 2 Marines for 6 IPCs, A4 D2 on amphibious assault will be better cost ratio than regular Infantry paired with Artillery A4 D4 C7.
But, in defense, 2 Marines Defense @2 cannot hold the ground as 2 Infantry Defense @4.
And also 2 Marines being weaker if going inland combat by themselves because of the no pairing bonus with artillery. But they stay on par 1:1 compared to a single Infantry on offense.
Also, in amphibious assault, Marines will be probably taken amongst first casualties compared to regular infantry because it is the same attack factor than Inf with Artillery (but have a lesser defense factor (very low 1), unless you keep them to move on a Cruiser or BB and want to spare TP to turn back home for new supply on next turn. So, such Marines unit will more often die during debarkment and regular Infantry will last longer, in anticipation of next assault going inland.
About Infantry moving NCM only with Cruiser or Battleship, it cannot simulate the initiative and offensive role being taken by Marines such as Guadalcanal.
As far as I understand, Marines were first almost everywhere in PTO while regular army troopers were mopping behind Marines and garrisoning conquered islands. Maybe the exception is Peleliu in Palau islands.