early F-4 variants were armed only with missiles in the 1960s. High casualty rates during the Vietnam War caused the US to reintroduce autocannon and traditional dogfighting tactics but the missile remains the primary weapon in air combat. In the Falklands War British Harriers, using AIM-9L missiles were able to defeat faster Argentinian opponents. Since the late 20th century all-aspect heat-seeking designs can lock-on to a target from various angles, not just from behind, where the heat signature from the engines is strongest. Other types rely on radar guidance (either on-board or "painted" by the launching aircraft). Use of air-to-air missiles as surface-to-air missiles In 1999 R-73 missile were adapted by Serb forces for surface to air missiles. The Houthi movement Missile Research and Development Centre and the Missile Force have tried to fire R-27/R-60/R-73/R-77 against Saudi aircraft. Using stockpiles of missiles from Yemeni Air Force stocks. The issue for the R-27 and R-77 is the lack of a radar to support their guidance to the target. However the R-73 and R-60 are infra-red heat seeking missiles. They only require, power, liquid nitrogen "to cool the seeker head" and a pylon to launch the missile. These missiles have been paired with a "US made FLIR Systems ULTRA 8500 turrets". Only one near miss has been verified and that was a R-27T fired at Royal Saudi Air Force F-15SA. However the drawback is that these missiles are intended to be fired from one jet fighter against another. So the motors and fuel load are smaller than a purpose built surface to air missile. For the West the Norwegian-American made NASAMS rely on using AIM-9 Sidewinder, IRIS-T and AMRAAM (the ER version) missiles to intercept targets. None of these missiles require modifications and hence it can take missiles straight from an aircraft. However NASAMS remain a concept that is yet to be combat tested, it has only successful engaged a simulated cruise missile. If deployed to Ukraine it will be the first time that this missile system has been used in combat. Warhead A conventional explosive blast warhead, fragmentation warhead, or continuous rod warhead (or a combination of any of those three warhead types) is typically used in the attempt to disable or destroy the target aircraft. Warheads are typically detonated by a proximity fuze or by an impact fuze if it scores a direct hit. Less commonly, nuclear warheads have been