Under the $910m programme, the aircraft has received new liquid crystal displays, radio altimeter, autopilot, digital flight director and other computer module updates.
The Block 45 modification upgrades or replaces 63 items including analogue instruments that are considered high-maintenance, the USAF said in a statement.
Air Force Life Cycle Management Center Legacy Tanker Division commander colonel Mark Mocio said: “This is the capstone modification that takes your 1950s / 1960s-era tanker and makes it a 21st-century asset that’s as modern as any flight deck we have in the Air Force.
“It enables us to meet all the global rules we have on air traffic navigation now and for a long time to come.”
The programme was started almost seven years ago to extend the service life of the USAF's ageing C/KC-135 series aircraft.
The Block 45 modification is said to enhance the previous PACER CRAG cockpit and fuel management systems upgrade accomplished between 1997 and 2001.
Powered by four CFM International CFM-56 turbofan engines, the KC-135 Stratotanker has been designed for aerial refuelling and airlift. The 136ft-long aircraft can carry up to 83,000lb of cargo.
This military aerial refuelling aircraft can accommodate a crew of three people, including pilot, co-pilot and boom operator.
Image: The flight deck of a KC-135R Stratotanker after completing the Block 45 avionics upgrade. Photo: courtesy of US Air Force photo / Greg L. Davis.