The United States Air Force announced last week that it will proceed with upgrades of probably more than three hundred F-16 fighter jets to compensate for an expected two year delay in combat readiness of the F-35A Joint Strike Fighter.

The F-35A, the conventional takeoff and landing version of Lockheed Martin’s fifth-generation fighter aircraft, isn’t expected by the Air Force to enter service until 2018. The Marine Corps anticipates that the F-35B vertical takeoff and landing variant will enter service late 2014 or in 2015.

The F-35 is supposed to replace the aging American F-16 fleet as well as the A-10 and most F/A-18 fighters. The Air Force and Navy fly many hundreds of these planes and were slated to buy more than 2,400 new fighter jets. The individual price tag of the planes has skyrocketed however. It is estimated that the F-35 will cost $133 million a piece and be far more expensive in maintenance than existing warplanes.

Last year, the Department of Defense disclosed that the entire program had exceeded its original cost estimate by more than 50 percent. Total expenditures could reach up to $1 trillion.

Delays have forced the military to buy upgraded versions of older F-15s and F-16s to make up for the temporary shortfall. Other nations, including Australia and Israel, will likely face similar “fighter gaps” and ask to lease American jets to make up for it — putting further pressure on the United States Air Force and Navy.

Some five hundred F-15s could remain in the air beyond 2030 under current plans by which time the youngest models will be almost fifty years old. Three hundred F-16s could last through the 2020s, averaging forty years in service. Of the Air Force’s 2,000 fighter jets, less than two hundred F-22 Raptors are on the cutting edge of aviation technology.