The F-35 Lightning II is becoming the primary fighter jet tasked with defending the skies of US allies in Europe and the Pacific. The jet is being integrated with other allied fighter jets (like F-15s, Typhoons, and F-16s) and air defense assets. The F-35 is an incredibly complicated system, and when a country purchases it, that country becomes more integrated into the US-led alliance. Countries that purchase the jet today must continue working with the United States for decades to keep the jets operational.