An obviously staged photo of an 11th Armored Cavalry M551, along the border between Ost und Westen Deutschland, May 1979. U.S. Army photo.
The M551 Sheridan was not considered a main battle tank, it was officially a Armored Reconnaissance/Airborne Assault Vehicle, beginning service with the U.S. Army in 1967.
A too clean looking 11th Armored Cavalry M551, West Germany, May 1979. USA photo.
Made out of mostly aluminum (the outer hull was ‘high density foam’ encased in aluminum), it was meant to be air droppable and amphibious.
Another obviously staged USA photo, border of Ost und Westen Deutschland, May 1979.
The 152mm main gun could fire low velocity HEAT (High Explosive Anti-Tank) or ‘canister’ rounds, or the Shillelagh anti-tank guided-missile. The low velocity rounds were useless against fast moving and distant enemy tanks, and by the 1970s the U.S. Army had newer and better anti-tank missiles, so the Sheridan got relegated to other jobs like playing the bad guy in war games, or posing for propaganda photos.
“Halt!”
The U.S. Army began reducing its inventory of M551s in 1978, retiring it from front line use in 1996. Remaining Sheridans were relegated to the role of bad guy for war games, being modified to look like various types of Soviet tanks. Finally, in 2003 it was retired from the OpFor (Opposition Forces) role.
Cold War 1961: 
BERLIN KRISE, ‘GAME OF CHICKEN’ M48A1 VS. T-54/55!