This coin is 1 9/16 inches in diameter.  This is a much older Military Airlift Command (MAC) challenge Coin. Predates 1991.

C-17 Special Operations Low Level II

SOLL II C-17s are operated out of Charleston Air Force Base, South Carolina, by the Special Operations Division of the 437th Airlift Wing, USAF Air Mobility Command (AMC). SOLL II operators are on constant alert, or 'J-Alert', ready at a moments notice for Joint Chief of Staff (JCS) tasking.

C-14 SOLL II Operations

Known C-17 SOLL II operations include:

• Afghanistan, November 2001 
  With the SOF war well underway, SOLL II C-17s flew insertion and supply flights for the 15th Marine Expeditionary Unit (MEU) who had taken over an austere desert airstrip known as LZ Rhino. The C-17s delivered 2.9 million pounds of cargo and 481 ground combat troops in 8 days, firmly cementing the US presence on the ground. 
  
  
• Iraq - March 2003
  In the opening moves of Operation Iraqi Freedom, coalition SOF secured a large airfield complex, known as H1, in the Western Iraqi desert. SOLL II C-17s airdropped SOF - including Rangers - as part of an air assault to secure the base. They also dropped engineering equipment which was subsequently used to clear and prepare the runways for use. At least one SOLL II C-17 later landed and acted as a Forward Area Refueling Point (FARP). Fitted with internal fuel bladders, the C-17 FARPs were used to refuel other SOF aircraft - both fixed and rotary wing - now operating from the captured H1 airfield. SOLL II birds would later transport a number of M1A1 Abrams tanks to H1 which would go on to support Delta Force operations in the area..
• REF: (.https://www.americanspecialops.com/usaf-special-operations/special-operations-low-level/)