During the 1960s, as strategic awareness increased and a multitude of alternative fighter designs were developed by Warsaw Pact and NATO members, the Lightning's range and firepower shortcomings became increasingly apparent. The transfer of McDonnell Douglas F-4 Phantom IIs from Royal Navy service enabled these much longer-ranged aircraft to be added to the RAF's interceptor force alongside those withdrawn from Germany as they were replaced by SEPECAT Jaguars in the ground attack role. The Lightning's direct replacement was the Tornado F3s, an interceptor variant of the Panavia Tornado. The Tornado featured several advantages over the Lightning, including a far larger weapons load and considerably more advanced avionics. Lightnings were slowly phased out of service between 1974 and 1988. In their final years the airframes required considerable maintenance to keep them airworthy due to the sheer number of accumulated flight hours.