One of the most important modifications to the KC-135 fleet is an engine retrofit, which for the last 20 years has been swapping the aircraft's Pratt&Whitney TF33 and Pratt&Whitney J57 powerplants with more modern and quieter General Electric/SNECMA F108s. The engine is built around the same core as the civil CFM56, which powers the Boeing 737-300, -400 and -500 airliners.

Although it is no longer the prime contractor for KC-135 programmed depot maintenance (PDM), Birmingham, Ala.-based Pemco Aeroplex continues to play a major role in the program under a subcontract to Boeing. As Boeing's huge San Antonio facility books more government work, particularly on the C-17 transport and the KC-10 tanker/transport, more KC-135 PDM is likely to be sent to Pemco.

Despite the advancing age of most of its variants, the C-130 Hercules continues to soldier on, and even now is playing a prominent role in the U.S. war on terrorism.