The Marine Corps just re-adopted the 1911 as the M45 in .45 ACP.
The USMC never fully "un-adopted" the 1911. There is a small specialized group of Marines (a few thousand) that have been using the 1911 all along. They practice a lot and Marine armorers have been rebuilding the WW2 guns again and again, using many modern parts that we use in our 1911s.
Once the WW2 guns were too worn from shooting and rebuilding, USMC had a contest and Colt won the contract for the M45. But most Marines will not ever use one, or probably even see one.