M551 Sheridan

This is the VISMOD T-80 (Visually Modified) that was used by OPFOR (Opposing Forces) Fort Irwin, California from 1981 until 2000 (or so) and was phased. Due to lack of parts and changes in OPFOR doctrine change in the early 2000's.
The Tank Commander wears US 3-color DCU's, which would place this photo in the 1990's. Since DCU's began to be issued in late 1991 or early 1992 and worn until 2001/2002.

Upon looking closer, the unit I.D. on the front,
177 BDE
1-63
Would place this photo prior to Oct. 24, 1994 (between 1992-1994) when the 177th Armored Brigade (Separate) was reflagged as the 11th ACR and 1st Battalion, 63rd Armor Regiment became 1st Squadron, 11th ACR.
*1-63 was the notional 125th Tank Regiment of OPFOR, the 177th being the notional 32nd Guards MRR.