I've been trying to get an idea of the overlap of front-line service of the M1 and the PASGT, and I'm finding that it was significant.
Below is a shot of US troops on Grenada during Operation Urgent Fury in
October of 1983. Soldiers on the left are in the venerable M1; the soldier on the far right is wearing the PASGT.
Here is a photo of the April 1985 Operation Bright Star, a recurring exercise between the United States and Egypt. The soldier to the left of the flag is wearing the PASGT, everyone else is wearing the M1. It is noteworthy that the M1s have the six-color "chocolate chip" cover deployed. Close examination of seams indicates that those are PASGT covers being used on the M1s.
This shows that there was a simultaneous front-line deployment of both helmets for at least eighteen months.
