Although no service has issued a requirement for an upgraded engine, Pratt and Whitney is cooperating with the US Navy on a two-block improvement plan for the F135 engine. The goals of Block 1 are a 7–10% increase in thrust and a 5–7% lower fuel burn. The plans include better cooling technology for turbine blades; this would increase the longevity of the engine and substantially reduce maintenance costs. The goal of Block 2 is to work with the US Air Force's Adaptive Engine Transition Program, with the intention of introducing technology for an engine rated at 45,000 lb of thrust, to be used in a sixth-generation fighter.