Turkey's armed forces have committed to purchasing 100 U.S. built F-35A fighters to modernise the capabilities of its Air Force. The fighter represents a critical pillar of the country's military modernisation program, with the F-35 as of yet the only fifth generation platform made available for export and the world's only fifth generation light fighter. It was designed as a next generation equivalent to the F-16 and F-5, a light, widely exportable and less costly complement to the heavier and more specialised F-22 Raptor - just as its predecessors were to the F-15 and F-4 respectively. With Turkey a longstanding client for U.S. arms, one of the world's largest operators of the F-16, and one of the five largest militaries in NATO, it was to be expected that Ankara would be one of the F-35's leading clients. Ankara has has of yet allocated funds for&nbsp;only 30 F-35A fighters, and future orders may well be based on the Air Force's evaluation of the performance of the first batch of fighters. There is a significant risk however that Turkey could well see delivery of the U.S. made fighters cancelled. Ankara's decision to purchase the Russian made S-400 Triumf air defence system rather than a Western made platform, despite growing tensions between NATO and Russia and a significant U.S. campaign to undermine Russian arms exports, has led Washington to threaten severe repercussions should Turkey proceed with the acquisition. Western analysts have also noted the risk that Russian made radars' deployed with the S-400 would cover Turkish airspace - potentially providing Russia with information critical to countering the F-35's stealth capabilities. Another threat to the sale has come from Greek and Armenian lobbies in the United States which have campaigned strongly for the cancellation of F-35 sales to Turkey. With both counties having significant historical animosities towards Ankara, and neither state in a position to similarly modernise its own Air Force, both have significant incentives to seek to deny Turkey such text generation capabilites. U.S. lawmakers have sought to hold the F-35 fighters to ransom should Ankara proceed with the multi billion dollar deal with Russia to acquire the S-400. Volkan Bozkir, chairman of the Turkish parliament's committee on foreign affairs, stated regarding the intentions held by many in the American leadership: "The U.S. attaches great importance to the issue of the S-400s, and Congress has a desire to link the S-400 sale with the sale of its F-35s. In the sense that if we buy the S-400s, Congress will decide to ban the sale of F-35s."Whether or not Turkey's acquisition of the F-35 will proceed remains to be seen, but Washington faces significant risks should it deny Ankara the fighters it has requested. The&nbsp;U.S. has already seen several of its former arms clients turn to alternative sources, primarily Russia, due to its unwillingness to provide them with more advanced or heavier fighters. Egypt, Indonesia, the UAE and Pakistan are all key examples of this. Should the U.S. deny Turkey the F-35, it will serve as an excellent pretext for Ankara to turn to Russia for a modern fighter aircraft to complement its Russian made air defences. The U.S. will lose several billion dollars in arms exports as well as further worsening relations with one of its key strategic partners and undermining the F-35 program. Turkey has long been unable to acquire modern air superiority fighters from the West and still relies on third generation F-4 Phantoms as its heaviest and most elite combat platform, while Russia has proven itself highly willing to export such fighters including its more advanced platform, the Su-35, even to longstanding Western partners.&nbsp;Having already turned to Russia and South Korea to provide weapons where Western suppliers have fallen short, potential for Turkey to induct its first non Western fighters into service remains significant - and would be spurred further should the U.S. deny the country the F-35. Ultimately the risks of withholding the F-35 from Turkey are likely to far outweigh the benefits.