The Hydra 70 rocket is a 2.75-inch (70 mm) diameter fin-stabilized unguided rocket used primarily in the air-to-ground role. It can be equipped with a variety of warheads, and in more recent versions, guidance systems for point attacks. The Hydra is widely used by US and allied forces, competing with the Canadian CRV7, with which it is physically interchangeable.

The Hydra 70 is derived from the 2.75-inch (70 mm) diameter 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. The Mk 40 was used during the Korean and 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, 1,335 pounds-force (5,940 N) (Mod 2/3) 1,415 pounds-force (6,290 N) (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.^[3]

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.

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 settable fuzes using the "wall-in-space" concept or fixed standoff fuzes.
• Training warheads.

Common warheads

The most common warhead for the Hydra 70 rocket is the M151 "10-Pounder," which has a blast radius of 10 meters and lethal fragmentation radius of around 50 meters.^[5]

This section does not cite any sources. (September 2017)

More information Designation, Description ...

Designation	Description	Weight	Payload	Fuze Type	Fuzing options
M151	High explosive (HEDP) '10 pounder'	8.7 pounds (3.9 kg) (w/o Fuze)	2.3 pounds (1.0 kg) Comp B-4 HE	M423	1,2,5,7,8
M156	White phosphorus munitions (WP)	9.65 pounds (4.38 kg)	2.2 pounds (1.00 kg) WP	M423 M429	1,2,6,7
M229	High explosive (HEDP); elongated M151 '17 pounder'	17.0 pounds (7.7 kg) (Fuzed)	4.8 pounds (2.2 kg) Comp B-4 HE	M423	1,2,6,7
M247	High-explosive anti-tank (HEAT)/high-explosive dual purpose (HEDP)	8.8 pounds (4.0 kg)	2.0 pounds (0.91 kg) Comp B HE	M438 PD	4 (integral to warhead)
M255	APERS (anti-personnel) warhead		2500 28 grains (1.8 g) flechettes		9
M255E1/A1	Flechette warhead	14.0 pounds (6.4 kg)	1179 60 grains (3.9 g) flechettes	M439	9
M257	Parachute illumination	11.0 pounds (5.0 kg)	One M257 Candle (Flare) 1 million candela	M442	10 (integral to warhead)
M259	White phosphorus (WP)				9
M261	Multi-purpose submunition (MPSM)	13.5 pounds (6.1 kg)	9 M73 (Grenade) Submunitions	M439 with M84 electric detonator	9
M264	Red phosphorus (RP) Smoke	8.6 pounds (3.9 kg)	72 RP Pellets	M439	9
M267	MPSM Practice	13.5 pounds (6.1 kg)	Three Marking SMs, 6 Metal Weights	M439 with M84 electric detonator	9
M274	Practice (Smoke)	9.3 pounds (4.2 kg)	2 ounces (57 g) of potassium perchlorate and aluminum powder	M423	1
M278	Infra-red (IR) parachute illumination	11.0 pounds (5.0 kg)	One M278 IR Flare	M442	10 (integral to warhead)
M282	Multipurpose penetrator warhead	13.7 pounds (6.2 kg)	0.98 pounds (0.44 kg) PBXN-110	delayed
Mk 67 Mod 0	White phosphorus (WP)				1,2,6,7
Mk 67 Mod 1	Red phosphorus (RP)				1,2,6,7
WTU-1/B	Practice	9.3 pounds (4.2 kg)	Inert	None	None
WDU-4/A	APERS warhead	9.3 pounds (4.2 kg)	96 flechettes of unknown weight		12 (integral to warhead)
WDU-4A/A	APERS warhead[6]	9.3 pounds (4.2 kg)[6]	2205 20 grains (1.3 g) flechettes[6]	M405A2[6]	12 (integral to warhead)

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This section does not cite any sources. (May 2023)

• Weight: 13.6 pounds (6.2 kg)^[3]
• Length: 41.7 inches (1,060 mm)^[3]
• Burn time: 1.07 sec^[3]
• Average thrust (77 °F (25 °C)):
  • 1,335 lbf (5.94 kN) (Mod 2/3)
  • 1,415 lbf (6.29 kN) (Mod 4)^[3]
• 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

There are several design efforts to turn the Hydra 70 rocket into a precision guided munition (PGM) to produce a weapon with greater accuracy but at less cost than other guided missiles. These include:

• The BAE Systems Advanced Precision Kill Weapon System (APKWS) II
• U.S. Navy Low-Cost Guided Imaging Rocket (LOGIR)
• Lockheed Martin Direct Attack Guided Rocket (DAGR)
• The ATK/Elbit Guided Advanced Tactical Rocket – Laser (GATR-L)
• Raytheon TALON
• Forges de Zeebrugge SAL-Laser Guided Rocket (FZ275 LGR)^[7]

The APKWS was the first to be fielded in March 2012,^[8] and the TALON entered full rate production for the United Arab Emirates Armed Forces in September 2014.^[9]

The Turkish ROKETSAN Cirit is a similar missile compatible with 70 mm rocket launchers, but it was developed from scratch and doesn't use Hydra 70 components.^[10]

•  Australia − APKWS^[11]
•  Colombia^[12]
•  Croatia − Used on Bell OH-58D Kiowa helicopters^[13]
•  Egypt^[14]
•  India − APKWS^[11]
•  Iraq − APKWS^[15]
•  Japan^[14]
•  Jordan − APKWS^[11]
•  Kuwait^[12]
•  Lebanon − APKWS^[16]
•  Netherlands − APKWS^[11]
•  Nigeria − APKWS^[17]
•  Pakistan^[18]
•  Philippines − APKWS^[11]
•  Qatar − APKWS^[19]
•  Saudi Arabia^[18]
•  Singapore^[12]
•  Taiwan^[12]
•  Thailand^[20]
•  Tunisia − APKWS^[11]
•  Ukraine − Used on Mi-24 gunships^[21]
•  United Arab Emirates^[22]
•  United Kingdom^[12]
•  United States^[23]

• Roketsan Cirit
• U.S. Army Aviation and Missile Command
• CRV-7
• FFAR rocket 2.75 in (70 mm)
• SNEB rocket (68mm)
• Zuni 5 in (127 mm)
• Advanced Precision Kill Weapon System

• International Institute for Strategic Studies (15 February 2023). The Military Balance 2023 (1st ed.). Routledge. ISBN 978-1032508955.