High Velocity Aircraft Rocket
The High Velocity Aircraft Rocket, or HVAR, also known by the nickname Holy Moses, was an American unguided rocket developed during World War II to attack targets on the ground from aircraft. It saw extensive use during both World War II and the Korean War.
Design and development
The HVAR was designed by engineers at Caltech during World War II as an improvement on the 5-Inch Forward Firing Aircraft Rocket, which had a diameter warhead but an underpowered diameter rocket motor. The desire for improved accuracy from the flatter trajectory of a faster rocket spurred the rapid development. HVAR had a constant diameter for both warhead and rocket motor, increasing propellant from of Ballistite. U.S. Ballistite propellant had a sea level specific impulse of over, compared with about for the British Cordite, German WASAG and Soviet PTP propellants. Hercules Powder Company was the principal U.S. supplier of high performance extruded Ballistite propellants: 51.5% nitrocellulose, 43% nitroglycerine, 3.25% diethyl phthalate, 1.25% potassium sulfate, 1% ethyl centralite, and 0.2% carbon black. The propellant in U.S. and rocket motors consisted of a single large X-shaped cross-section, "cruciform" Ballistite grain cavity. This went against the common practice of filling rocket motors with different numbers of smaller same-sized tubular charges with a round cavity, the number depending on motor diameter. The central hole in a tubular charge makes it more difficult to extrude, requiring a softer propellant blend that also yields somewhat lower performance. Rocket ∆V increased from for the AR to for HVAR, giving the coveted flatter trajectory.Operational service
Two different versions of the HVAR were built during World War II. The warheads were Mk 4 general purpose warheads holding of TNT with base and optionally nose fuses; or Mk. 2 AP warheads with of Explosive D.HVAR testing was complete by D-Day, 6 June 1944, and air-lifted Navy HVAR rockets were soon being loaded on Ninth Air Force Republic P-47D Thunderbolts to support the break-out at Normandy. Other single-engine delivery aircraft included the Vought F4U Corsair, Grumman F6F Hellcat, Grumman TBF/TBM Avenger, and Curtiss SB2C Helldiver. Twin-engine aircraft sometimes armed with HVARs included the Lockheed P-38 Lightning, North American PBJ Mitchell bomber and the Lockheed PV-2 Harpoon bomber.
HVAR could penetrate 4 ft of reinforced concrete and was used to sink transports, knock out pillboxes and AA gun emplacements, blow up ammo and oil-storage dumps, and destroy tanks, locomotives, and bunkers. Navy F4U Corsairs and TBF/TBM Avengers made the most extensive use of the rockets in the Pacific theater after the victory in Europe. Over a million HVARs were made during World War II, and production continued until 1955. HVARs remained in the Navy's inventory until the mid-1960s. After World War II, newer versions included a new general purpose type with a proximity fuse, White Phosphorus smoke rounds, an anti-submarine head, and a new shaped-charge warhead for use against tanks. The 6.5 inch RAM rocket was an oversized shaped-charge head on a standard HVAR motor as well.
HVAR was an effective weapon in the hands of skilled, experienced pilots. It was less effective in the hands of average or inexperienced pilots who were accustomed to taking less careful aim and then "walking in" their gunfire to finally engage a target. HVARs could be fired in pairs or a single rapid-fire salvo but required accurate initial alignment and careful attention to range, or at least a good instinctive sense for the range to the target. HVARs were widely used in the Korean War. Douglas AD-1 Skyraiders often carried a dozen HVARs, and sometimes an additional pair of much larger but less accurate Tiny Tim rockets. Targets included ships, bunkers, pillboxes, coastal defense guns, ammunition dumps, and occasionally even destroyers and major bridges. Numerous North American F-51D Mustang "Six-Shooters" and carrier-based Grumman F9F Panther jets flew close air support in Korea. Panthers carried 6 HVARs and four 20mm cannons, while both planes could carry an additional pair of 500 lb bombs, napalm, or fuel tanks. Neil Armstrong and John Glenn were among the Panther pilots. It was in Korea that HVARs and Tiny Tims bridged the gap between prop planes and jets: Lockheed F-80C Shooting Star, Republic F-84E Thunderjet, Grumman F9F Panther, and North American F-86 Sabre. Jets gave the fighter pilots improved forward visibility. F-84E Thunderjets proved to be the most capable load-lifting fighter/bombers in Korea, demonstrating an ability to loft up to 24 HVARs and 2 Tiny Tims with a combined rocket weight of.
In April 1945, HVAR rockets were used in Operation Bumblebee in the Navy's facility on Island Beach, New Jersey. The HVAR rockets launched 6-inch ramjet engines from wooden frames, accelerating the carbon disulfide fuel ramjets to flight speed. On June 13, the ramjets achieved supersonic speed.
HVAR rockets were used in the 1970s, the Mk.32 HEAT round being used by Air Force A-1E Skyraiders in Vietnam
Warheads
Initial WW2 HVAR warheads were modified 5"/38 caliber gun shells, with the Mk.6 head being a modification of AA Common shells and the Mk.2 being derived from Special Common rounds. Later heads were purpose-built. The Mark 6 HE head came in two variations, Mod 0 and Mod 1. Mod 1 had a deep nose cavity to fit the M403 VT fuze and thus carried 0.5lb less explosive fill.| Type | Model | Weight | Filler | Filler weight, lb |
| HE | Mk 6 Mod 1 | 45.87 | TNT | 7.6 |
| HE | Mk 6 Mod 4 | 45.04 | TNT | 7.1 |
| AP | Mk 2 | 48.3 | Explosive D | 2.2 |
| Smoke-PWP | Mk 4 | 48.09 | PWP | 19.36 |
| HEAT | Mk 25 | 47.85 | Comp B | 15.33 |
| AP/ASW | Mk 29 | 48.56 | Explosive D | 3.03 |
Ammunition
A head assembled with a motor is known by a separate designation listed below.| Head | Complete Round | Type | Weight |
| Mk 6 Mod 1 | Mk 28 Mod 4 | GP | 138.49lb |
| Mk 6 Mod 4 | Mk 28 Mod 5 | VT | 138.49lb |
| Mk 25 | Mk 32 | HEAT | 140.47 |
| Mk 29 | Mk 34 | AP/ASW | 138.43lb |
| Mk 2 | Mk 35 | AP | 138.47lb |
| Mk 4 | Mk 36 | Smoke-PWP | 140.71lb |
Performance
| Ammunition Type | Concrete Penetration, '''0° | 30° |
| GP Mk 6 Mod 0 | 1,143mm | 838mm |