The RTV-A-2 Hiroc (high-altitude rocket) was a product of the United States' first effort to develop an intercontinental ballistic missile (ICBM).

[1][2] The design included several innovations; the gimbaled thrust chambers provided guidance control, the internal gas pressure was used to support the airframe and the nose cap was separable.

[3] The Hiroc missiles were 31.5 feet (9.6 m) long, had a fin span (the maximum width of the rocket, accounting for the fins) of 6 feet 10 inches (2.08 m), a diameter of 30 inches (760 mm), an empty weight including payload of 1,205 pounds (547 kg) and a gross liftoff weight (GLOW) of 4,090 pounds (1,860 kg).

[7] The gimbal system adds complexity to the engine mounting but preserves more of the energy of the rocket exhaust during maneuvering.

[4] The unique innovations of the Hiroc missiles, such as the gimbaled thrust chambers, and the internal pressure supported airframe, would go on to be utilized in the Atlas rockets.

[21] Although development of the specification MX-774B was inspired by the German V-2 the MX-774B introduced several significant innovations, such as an integrated propellant tank, swiveling engines, pressurized body, and detachable nose cone.

The project was eventually canceled in June 1947 as the Army concentrated their efforts on cruise missiles, which were more promising at that time.

Due to a mistake in packing, the payload recovery parachute failed to open; a camera and a few other instruments survived, so the test was deemed a partial success.

The parachute failed again, this time due to a battery problem; the Hiroc began to freefall before its oxygen tank exploded at 20,000 feet (6,100 m).

[28] All three Hiroc missiles had partially failed due to premature closure of the liquid oxygen valve.

The cause of the valve closing was traced to vibration of solenoids which caused pressure change in the hydrogen peroxide line which allowed nitrogen to vent from engine control lines with the resultant pressure drop closing the LOX valve.