Hydra 70 (2.75 in) rocket

A bomber-killer that missed

The 2.75 in rocket began as an answer to a Cold War problem. Jet bombers closed so fast that a fighter pilot had only a moment to fire, and wartime experience suggested that machine guns could not reliably bring a bomber down. The Germans had shown that volleys of unguided rockets could. [2] In the late 1940s the US Navy developed the Mk 4 Folding-Fin Aerial Rocket, about 4 ft long and 18.5 lb, whose fins flipped out as it left the tube. Crews called it “Mighty Mouse”, after the cartoon character. [2] In the early 1950s it was the main armament of interceptors such as the F-86DF-86 Sabre AircraftThe swept-wing day fighter that met the MiG-15 over Korea., F-89 and F-94C, carried in large numbers and fired in volleys. [2]

As an air-to-air weapon it was a disappointment. One hit could destroy a bomber, but the rockets scattered so widely that a 24-round volley covered an area the size of a football field. In August 1956 two Air Force F-89s fired 208 rockets at a runaway Navy target drone and failed to bring it down. By the end of the decade guided missilesGuided missile GlossaryWeapons: An unmanned vehicle moving above the surface of the Earth whose trajectory or flight path is capable of being altered by an external or internal mechanism. had replaced it. [2]

A second career

Against the ground, where a volley’s spread mattered less, the rocket found its true role, above all on the new armed helicopters. Fitted with the more powerful Mk 40 motor and a range of warheads, it served in Korea and Vietnam from about 20 different aircraft, fixed-wing and rotary. [1] [2] The Navy’s ordnance manual still notes that rockets began in aircraft armament in the Second World War because they gave a heavy blow without recoil, and that the Navy’s two rockets are the 2.75 in “Mighty Mouse” and the 5 in ZuniZuni 5 in rocket OrdnanceThe Navy's 5 in rocket of 1957, fired from four-tube LAU-10 pods and credited with an A-4 Skyhawk's only MiG kill.. [6] It describes FFARsFFAR GlossaryWeapons: Folding-fin aircraft rocket. The Navy's 2.75-inch rocket, known as the Mighty Mouse; the 5.0-inch folding-fin rocket is the Zuni. fired in large numbers to make a shotgun pattern, and a low-spin version for helicopters and low-speed aircraft which, because it spins, is fired one at a time rather than rippled. [4]

Hydra 70

The modern Hydra 70 is the same 2.75 in rocket with the Mk 66 motor. Its propellant gives considerably more thrust, its fins wrap around the body and flick sideways to open, and its slightly angled nozzles start it spinning while it is still in the tube. [1] The motor burns for just over a second and the rocket leaves the tube at 148 ft/s, reaching 2,425 ft/s at burnout. [1] The commonest warhead, the M151 “10-pounder”, is high-explosive fragmentation, the kind the Navy manual describes for use against troops and light targets such as trucks and parked aircraft. [1] [3]

Today it is carried by every US service. The Army fires it from ApachesAH-64D Apache Longbow AircraftThe US Army's twin-engine attack helicopter, flown from Panama and Desert Storm to Afghanistan; the Longbow adds a mast-mounted radar. in 19-tube M261 launchers and from KiowaOH-58D Kiowa Warrior AircraftThe US Army's armed scout helicopter, with its ball-shaped sight above the rotor, flown from the Persian Gulf to Afghanistan. Warriors in seven-tube M260s; the Marine Corps carries it on the AH-1W and AH-1Z and on the UH-1UH-1H Huey AircraftThe utility helicopter that defined the Vietnam War and served every US armed service; more than 16,000 built.; and the Navy and Air Force use it too. [1] The Navy’s launchers are the seven-tube LAU-68 and the 19-tube LAU-61, both reusable and able to fire singly or in ripple. [5]