After 22 years of development the United States military&nbsp;in 2014 began to induct its first F-35 fifth generation light fighters into service. The Marine Corps that year received the first F-35B fighters, and the Air Force has since received the first of its F-35As. The U.S. Navy's carrier based F-35C is set to enter service in 2019, and the three variants of the F-35 are set to replace the Navy's F-18, the Marine Corps' Harrier&nbsp;and&nbsp;the Air Force's F-16. The fighter is the most costly light multirole platform ever to enter service, with costs even exceeding those of high performance heavy fighters such as the F-15C and Su-35. What has been truly outstanding regarding the F-35 program however are its extreme maintenance requirements, both costly and time consuming as they are, and the severe performance defects which have resulted from its excessive complexity. While light multirole fighters such as the F-35's predecessors the F-16 were F-5 are prized for their low operational costs and low maintenance times, the new U.S. fighter appears to fail to fulfil these key criteria. The result is that while the U.S. Military can budget for the acquisition of new F-35 fighters, with over 2000 set to be built for the three services, it has largely failed to account for the added and far greater costs of maintaining these fighters over their decades long lifespans.Even with the relatively small contingent of F-35 fighters currently in service the military has struggled with maintenance - only 50% of fighters fielded today are currently serviceable. A report by the Pentagon's Director of&nbsp;Operational Test &amp; Evaluation to Congress in 2018 presented these figures, noting that half the F-35 fighters the military had inducted were inactive sitting in hangars rather than operational. This has a severe impact not only on the U.S. military's operational readiness, but also on the quality of its pilots. The U.S. Government Accountability Office has similarly noted that maintenance for the F-35 has left much to be desired, stating: "DoD's capabilities to&nbsp;repair F-35 part at&nbsp;military depots are six years behind&nbsp;schedule, which has resulted in&nbsp;average part repair times of&nbsp;172 days (six months) &nbsp;”” twice the program's objective," The GAO also found a severe shortage in&nbsp;spare parts for&nbsp;the aircraft. Their report further stated: "The F-35 aircraft represents the future of&nbsp;tactical aviation for&nbsp;the U.S. military, and is DoD's most expensive weapon system, with&nbsp;sustainment costs alone estimated at&nbsp;more than $1 trillion over&nbsp;a 60-year life cycle."Ellen Lord, the new Defense Department undersecretary for defense acquisition, has been one of the first to address the military's key challenge of sustaining the ever expanding F-35 fleet - stating that the military "can’t afford the sustainment costs we have on the F-35." According to&nbsp;the U.S. Joint Chiefs of&nbsp;Staff, "sustainment is a key component of&nbsp;performance. Including sustainment planning ”˜up front' enables the acquisition and requirements communities to&nbsp;provide a weapon system with&nbsp;optimal availability and reliability to&nbsp;the warfighter at&nbsp;value." As the U.S. military cannot afford to sustain the F-35 this will likely result either in the need to compromise flight hours, pilot training, and the quantity of fighters inducted into service - or to receive more funds either through significant expansions to the defence budget aimed solely at sustaining the Joint Strike Fighter or by diverting funds from other defence programs to the F-35. Which ever option is taken, it is clear that sustaining the military's latest and most complex fighter will prove a significant challenge in the following years which already has and is likely to continue to undermine combat readiness.