During the Cold War a great variety of aircraft evolved; not all of them saw action in the major conflicts of the period. Some were counterinsurgency aircraft, still others provided a nuclear deterrent, as the competing superpowers and their allies sought to remain vigilant against the actions of the other side. As aircraft capability increased, so too did their level of sophistication and cost of development, maintenance and deployment. For these reasons, it was often the case that military aircraft during the four-plus decades of the Cold War served long past their intended service life. Another outcome of spiraling development costs was the birth of the multi-role aircraft, starting in the 1960's with the General Dynamics FB-111, and continuing to present day with aircraft such as the McDonnell Douglas F/A-18 and the Panavia Tornado.