The RIM-174 Standard Extended Range Active Missile (ERAM), or Standard Missile 6 (SM-6), is a missile in current production for the United States Navy. It was designed for extended-range anti-air warfare (ER-AAW) purposes, providing capability against fixed and rotary-wing aircraft, unmanned aerial vehicles, anti-ship cruise missiles in flight, both over sea and land, and terminal ballistic missile defense. It can also be used as a high-speed anti-ship missile. The missile uses the airframe of the earlier SM-2ER Block IV (RIM-156A) missile, adding the active radar homing seeker from the AIM-120C AMRAAM in place of the semi-active seeker of the previous design. This will improve the capability of the Standard missile against highly agile targets and targets beyond the effective range of the launching vessels' target illumination radars. Initial operating capability was planned for 2013 and was achieved on 27 November 2013. The SM-6 is not meant to replace the SM-2 series of missiles but will serve alongside and provide extended range and increased firepower. It was approved for export in January 2017.

Anti-aircraft warfare is the counter to aerial warfare and it includes "all measures designed to nullify or reduce the effectiveness of hostile air action". It includes surface based, subsurface, and air-based weapon systems, associated sensor systems, command and control arrangements, and passive measures. It may be used to protect naval, ground, and air forces in any location. However, for most countries, the main effort has tended to be homeland defence. Missile defence is an extension of air defence, as are initiatives to adapt air defence to the task of intercepting any projectile in flight.