Hydra 70

The Hydra 70 rocket is a weapon derived from the 2.75 inch Mk 4/Mk 40 Folding-Fin Aerial Rocket developed by the United States Navy for use as a free-flight aerial rocket in the late 1940s.

Overview

The Hydra 70 family of WAFAR (Wrap-Around Fin Aerial Rocket), based on the Mk 66 universal motor, was developed from the previous 2.75 inch Mk 40 motor-based folding fin aerial rocket. The propellant grain is longer and of a different formulation than that of the MK40/MK4, however, the stabilizing rod and igniter are essentially the same design. The MK66 motors have a substantially higher thrust, 1,335 pounds-force (5,940 N) (Mod 2/3) 1,415 pounds-force (6,290 N) (Mod 4), and a longer range than the older motors. To provide additional stability the four rocket nozzles are scarfed at an angle to impart a slight spin to the rocket during flight. The Mk 40 was used during the Korean and Vietnam wars, being used to provide close air support to ground forces from about 20 different firing platforms, both fixed-wing and armed helicopters. Today, the OH-58D(R) Kiowa Warrior and AH-64D Apache Longbow, as well as the Marine Corp's AH-1 Cobra, carry the Hydra rocket launcher standard on its weapon pylons.^[3][4]

Mk 66 rocket motor variants

Service

Hydra 70 rockets on an AH-1 Cobra helicopter

The family of Hydra 70 (70 mm) 2.75 inch rockets perform a variety of functions. The war reserve unitary and cargo warheads are used for anti-materiel, anti-personnel, and suppression missions. The Hydra 70 family of folding-fin aerial rockets also includes smoke screening, illumination, and training warheads. Hydra 70 rockets are known mainly by either their warhead type or by the rocket motor designation, Mk 66 in US military service.

United States

In the U.S. Army, Hydra 70 rockets are fired from the AH-64A Apache and AH-64D Apache Longbow helicopters using M261 19-tube rocket launchers, and the OH-58D Kiowa Warrior using seven-tube M260 rocket launchers. In the U.S. Marine Corps, either the M260 or M261 launchers are employed on the AH-1 Cobra and future AH-1Z Viper, depending upon the mission. The M260 and M261 are used with the Mk 66 series of rocket motor, which replaced the Mk 40 series. The Mk 66 has a reduced system weight and provides a remote fuze setting interface. Hydra 70s have also been fired from UH-60 and AH-6 series aircraft in US Army service.

The AH-1G Cobra and the UH-1B "Huey" used a variety of launchers including the M158 seven-tube and M200 19-tube rocket launchers designed for the Mk 40 rocket motor; however, these models have been replaced by upgraded variants in the U.S. Marine Corps because they were not compatible with the Mk 66 rocket motor. The Hydra 70 rocket system is also used by the U.S. Navy, and the U.S. Air Force.

Common U.S. Mk 66 compatible launchers

Hydra 70s in an M261 launcher on a Dutch AH-64 Apache. The tips of some of the rockets are white (and the rockets are shorter in length) because they have a different type of fuze/warhead.

Warheads

Hydra 70 warheads fall into three categories:

• Unitary warheads with impact-detonating fuzes or remote-set multi-option fuzes.
• Cargo warheads with air burst-range, with setable fuzes using the "wall-in-space" concept or fixed standoff fuzes.
• Training warheads.

Fuzing options

Common warheads

NOTE: Though some of the warheads described were designed for the older Mk 40 rocket motor, but most likely could work with the Mk 66 motor if upgraded or modernized models were not available. However, this would not be necessary, as vast quantities of upgraded models exist today.

Mk 66 rocket motor technical data

Weight: 13.6 pounds (6.2 kg)

Length: 41.7 inches (1,060 mm)

Burn time: 1.05–1.10 sec

Average thrust (77 F):

• 1,335 lb (Mod 2/3)
• 1,415 lb (Mod 4)

Motor burnout range: 1,300 feet (400 m)

Motor burnout velocity: 2,425 ft/s (739 m/s)

Launch spin rate: 10 rps, 35 rps after exiting launcher

Velocity at launcher exit: 148 ft/s (45 m/s)

Acceleration:

• 60–70 g (initial)
• 95–100 g (final)

Effective Range: 547 to 8,749 yards (500 to 8,000 m) depending on warhead and launch platform

Maximum Range: 11,483 yards (10,500 m) under optimum conditions

Precision guided Hydra 70

The Advanced Precision Kill Weapon System (APKWS) II is a program to provide a laser guidance to the existing Hydra 70 systems in service. It was cancelled by the US Army in February 2007,^[5] but was restarted by the US Navy in 2008. Similar programs are the US Navy Low-Cost Guided Imaging Rocket, Lockheed Martin Direct Attack Guided Rocket and the ATK/Elbit Guided Advanced Tactical Rocket – Laser. APKWS has been fired successfully from the AH-64 Apache by BAE Systems in trials at Yuma Proving Grounds in early September, 2013; US Navy trials of the APKWS with the A-10 Thunderbolt II, the AV-8B Harrier and the F-16 Fighting Falcon led to US Central Command's approval of a modified version of APKWS to be fired from fast-moving jet aircraft.^[6]

Users

•  Australia
•  Colombia
•  Japan
•  Kuwait
•  Netherlands
•  Philippines,^[7] The launchers are mounted on AS-211 "Warrior" trainers with secondary combat capability and 520MG Defender helicopters.^[7]
•  Singapore
•  Thailand
•  United Arab Emirates
•  United Kingdom
•  United States
•  South Korea
•  Egypt

See also

• U.S. Army Aviation and Missile Command
• CRV-7
• FFAR rocket 2.75 in (70 mm)
• SNEB rocket (68mm)
• Zuni 5 in (127 mm)

References

External links

• "Hydra 70". GlobalSecurity. Retrieved 2005-09-01. 
• Hydra-70 Rockets: From Cutbacks to the Future of Warfare, Defense Industry Daily, April 2006 .
• Air-Launched 2.75-Inch Rockets, Designation Systems .
• "Hydra-70", Warheads energetics, Weapon Systems, General Dynamics .
• 2012 Army Weapon Systems Handbook