Editing Hydra 70 (section)

==Overview==
The Hydra 70 is derived from the {{convert|2.75|in|mm|abbr=out|adj=on}} diameter Mk 4/Mk 40 [[Folding-Fin Aerial Rocket]] developed by the [[United States Navy]] for use as a free-flight aerial [[rocket (weapon)|rocket]] in the late 1940s. The Mk&nbsp;40 was used during the [[Korean War|Korean]] and [[Vietnam War|Vietnam]] wars to provide close air support to ground forces from about 20 different firing platforms, both fixed-wing and armed helicopters.

The main change made to produce the Hydra was the Mk. 66 motor which uses a new propellant that offers considerably more thrust, {{Convert|1335|lbf}} (Mod 2/3) {{Convert|1415|lbf}} (Mod 4). The fins of the Mk 40 flipped forward from the rear when the rocket left the launching tube, but in the Hydra they are curved to match the outside diameter of the rocket fuselage and flip sideways to open, which is referred to as WAFAR (Wrap-Around Fin Aerial Rocket) instead of FFAR (folding-fin aerial rocket). To improve stability during the time the fins are still opening, the four motor nozzles have a slight cant angle to impart a spin while the rocket is still in the launch tube.

Today, the OH-58D(R) Kiowa Warrior and AH-64E Apache Longbow, as well as the Marine Corps' versatile UH-1 Huey and AH-1 Cobra, carry the Hydra rocket launcher standard on its weapon pylons.<ref name=":1">{{citation |publisher=GDATP |url=http://www.gdatp.com/files/PDF/A064_Hydra-70.pdf |title=Hydra 70 |access-date=6 August 2010 |archive-url=https://web.archive.org/web/20100704231453/http://www.gdatp.com/files/PDF/A064_Hydra-70.pdf |archive-date=4 July 2010 |url-status=usurped }}.</ref>

===Mk 66 rocket motor variants===
{|class="wikitable" style="font-size:96%;"
! style="width: 7em;" | Designation
! Description
|-style="vertical-align: top;" |
|Mk 66 Mod 0
|70&nbsp;mm (2.75&nbsp;in) WAFAR universal motor; common motor for the GD Hydra 70 series of rockets; original prototype; for US Army
|-style="vertical-align: top;" |
|Mk 66 Mod 1
|Mk 66 variant; production variant; for US Army
|-style="vertical-align: top;" |
|Mk 66 Mod 2
|Mk 66 Mod 1 variant; HERO (Hazards of Electromagnetic Radiation to Ordnance) safe; for US Navy and US Air Force
|-style="vertical-align: top;" |
|Mk 66 Mod 3
|Mk 66 Mod 1 variant; HERO safe; Mk 66 Mod 2 for US Army
|-style="vertical-align: top;" |
|Mk 66 Mod 4
|Mk 66 Mod 2/3 variant; incorporates a Salt rod to reduce exhaust gases; for all services
|-style="vertical-align: top;" |
|Mk 66 Mod 5
|Mk 66 Mod 4 variant; Incorporates propellant venting during fast cook off
|-style="vertical-align: top;" |
|Mk 66 Mod 6
|Mk 66 Mod 4/5 variant; designed to reduce the tendency of secondary launch gases to combust in the parent aircraft’s engine, primarily with the AH-64 helicopter
|}