The US and Britain spent 20 years secretly pretending to be at war with each other to help develop defences against the Soviets.

Alarmingly during Operation Skyshield, the British managed to get 7 out of 8 nuclear bombers over their designated targets on the US East Coast including New York, due to more advanced ECM blocking US radar and evasion tactics of the Vulcan bombers and their crews. Something previously thought impossible. Thankfully the lessons learned from these repeated operations on both sides of the Atlantic prevented a deterrent becoming a course of action.