The US Marine Corps appear as a friendly faction in all United States based missions. They are mostly only present for teh asthetics, but in Red Glare, they play a prominent role in escorting Delta and the civilians. The last Marines are seen in Endgame, where they hold their position in Central Park against Russian Ground Forces.
The US Marine Corps reappear in Iron Wolf as a friendly faction. They are only present aboard the USS Equilibrium, the last remaining carrier of the United States. Marines appear in 121 Stories, where they launch the coastal assault on Inagua, the Bahamas. After that, some Marines appear in cutscenes.