Miramar Marine Corps Air Station

When did Miramar become an MCAS? It used to be the main NAS on the west coast and housed Top Gun. What happened to it?

It was transfered to the marines when they closed El Toro

It mostly had a lot to do with the military cutbacks and the whole Navy training system. While Fighter Weapons School (TopGun) was at Miramar, Naval Strike and Air Warfare Center (then called just Naval Strike Warfare Center) was based at NAS Fallon in Nevada. Even with cutbacks, it was common sense that it was a waste of money to have two similar Navy fighter training schools in two different locations. Since NSWC was much larger and was located in a place more suitable for combat training (San Diego is not good for air combat), they took the smaller program (NFWS) and consolidated both programmes at Fallon. That's why it's called Naval Strike and Air Warfare Center, because the two programs are in conjunction now, even though they are executed separately.

They in turn closed the large MCAS El Toro and moved it to Miramar.