The McDonnell Douglas Helicopter Systems MD 500 Defender is a light multi-role military helicopter based on the MD 500 light utility helicopter and OH-6 Cayuse Light Observation Helicopter. The original OH-6 Cayuse helicopter proved its worth during the Vietnam War in the light helicopter role. The designers at Hughes realized there was a market for a light multi-mission helicopter with an improved equipment fit than the OH-6 and Model 500M. The resulting design was the Model 500MD Defender which first flew in 1976. It was tailored for specific roles including unarmed observation and an armed scout helicopter equipped with TOW anti-tank missiles. An anti-submarine version was developed with a search radar, magnetic anomaly detector and the capability to carry lightweight aerial torpedoes.
