For the F-35, this is roughly the equivalent of asking why Google or Facebook doesn&#x27;t use COTS software instead of mess of proprietary legacy code.<p>The F-35&#x27;s reason for existence is its software. Other existing aircraft are faster, can carry more, fly further, or be more stealthy. The F-35&#x27;s value statement is that its pilots will know more about what&#x27;s going on around it than any other combat aircraft, for the next ten or fifteen years.<p>COTS stuff is used at the base layers of military avionics. LynxOS is used under the hood of the Army&#x27;s very successful CAAS helicopter avionics system.