| M8 | |
|---|---|
 M8 rockets being launched from a "Calliope" multiple launcher mounted on a Sherman tank. | |
| Type | Air-to-surface and surface-to-surface rocket |
| Place of origin | United States |
| Service history | |
| Used by | United States Army,United States Navy |
| Production history | |
| Designer | Picatinny Arsenal |
| Designed | 1941 |
| Manufacturer | Chrysler Corporation,Highland Park Plant (328,327);[1]Hercules Powder CompanyRadford Ordnance Works andSunflower Ordnance Works (solvent powder)[2] |
| Produced | 1941-1944 |
| No. built | 2,537,000[3] |
| Specifications | |
| Mass | 38 lb (17 kg) |
| Length | 33 in (840 mm) |
| Diameter | 4.5 in (114 mm) |
| Warhead weight | 4.3 lb (2.0 kg) |
| Engine | Solid-fuel rocket 4.75 lb (2.15 kg) fuel |
Operational range | 4,600 yd (4.2 km) |
| Maximum speed | 600 mph (970 km/h) 880 ft/s (270 m/s) |
Guidance system | None |
Launch platform | Republic P-47,Lockheed P-38G Lightning,M4 Sherman,LST |
TheM8 was a 4.5-inch (114 mm)rocket developed and used by the United States military duringWorld War II. Produced in the millions, it was fired from both air- and ground-based launchers; it was replaced by theM16 rocket in 1945.
The first modern research into militarysolid-propellant rockets in the United States was conducted by ColonelLeslie Skinner at theAberdeen Proving Ground in 1932. Little interest was shown by the US Armed Forces however, until the introduction of a Britishanti-aircraft rocket;[4] both nations exchanged their research data before the United States entered World War II.[5]
The M8 rocket was developed by theNational Defense Research Committee and theArmy Ordnance Department in the early 1940s[6] atPicatinny Arsenal.[7] The specifications were agreed in the summer of 1941 after examining equivalent British rockets. Skinner produced the first prototypes which were tested at Aberdeen that fall, improvised from oldfire extinguisher tanks for rocket casings, thereby determining the 4.5 inch diameter.[8] It wasstabilized by base-hinged flip-out fins on the tail, a system patented byEdgar Brandt in 1930[9] (and also used on GermanR4M rocket), which proved less than satisfactory for ground-launched rockets as their initial low velocity and resulting low fin forces led to wandering in the first moments of flight.[10] (Modern implementations of this system like theRPG-7 grenade launcher spin the projectile before leaving the tube to prevent that.)
Original priority was given to an air-to-ground version. Confidence in the initial results was so high that theUSAAF had ordered 3,500 rockets before any had been actually fitted to an aircraft and it was hoped to have them operational in time forOperation Torch, the invasion of North Africa, in October 1942. The successful launch of an M8 from aCurtiss P-40E fighter on 6 July 1942 resulted in a procurement order for 600,000 units. Development began on a reloadablelauncher that could be fitted in the bomb bay of aDouglas A-20 bomber, but this never became operational. There were considerable problems with the propellant, the fuses and the underwing launching tubes, all of which considerably delayed operational deployment.[8]
The initial production model was given the Army designation of M8; improvements resulted in the M8A3, with a more powerful rocket engine and enlarged fins,[3] and the T22, which had improved reliability and modifications to make the rocket safer.[6]
Entering service in 1943, the M8 family of rockets saw service with theUnited States Army, which classified the M8 as a "barrage rocket".[6] The rocket was also widely used by theUnited States Army Air Forces.[6] Over 2,500,000 of the M8 type rocket had been produced by the end of the war.[3]
Operational service showed some drawbacks in the M8's performance; ground launch resulted in the rockets' fin stabilizers proving ineffective,[10] reducing the accuracy of the rocket; despite this, it was considered an effective barrage weapon.[11] Due to the lack of accuracy, when ground-launched, it was being launched from largemultiple launchers; the most commonly used being eight- and 60-tube launchers, called "xylophones" and "calliopes" respectively.[3][6] The officially-named U.S. ArmyT34 Calliope launch system was mounted on top of aM4 Sherman tank; once fired, the launcher could be detached and discarded, allowing the tank to be used in conventional combat, while the "xylophone", officially the T27, was carried on a 2½-ton truck's cargo bed.[3] A 120-round launcher, designated T44, and a 144-round T45 launcher were also developed; these were intended for use by theUnited States Navy, being mounted onDUKW amphibious vehicles andLST amphibious warfare vessels. Single- and twin-14-round launchers were also developed.[3]
The M8 showed poor effectiveness against hardened targets;[6] this resulted in the development of the Super M8, which had larger fins, a more powerful rocket and a more powerful warhead. The Super M8 underwent testing in late 1944, but failed to see combat.[6] The M8 was replaced by the improved spin-stabilizedM16 rocket during 1945.[3][10]
The method of launching the M8 from the wings of fighters were finally solved by the development of an M10 triple-tube launcher made of plastic or alloy. However, the modification required to adapt existing aircraft to carry these launchers was vastly more complicated than that required for the 5-inchHigh Velocity Aircraft Rocket (HVAR) or "Holy Moses" which had been developed by theUS Navy and was better in some respects than the M8 in performance. The M8 was initially available in greater numbers than the HVAR,[8] and was fitted toLockheed P-38 Lightnings[12] andRepublic P-47 Thunderbolts of the USAAF in Italy, Northwest Europe, south-east Asia and Pacific theatres from the second half of 1944, before being gradually replaced by the HVAR. However, the air-launched rocket was never a popular weapon with US fighter-bomber squadrons in Europe.[13]
| 5" HVAR Rocket | 4.5" M8 Type Rocket | |
|---|---|---|
| Total weight | 140 pounds (64 kg) | 40 pounds |
| Maximum velocity | 1,300 feet per second (400 m/s) | 865 feet per second |
| Weight of high explosive | 7.8 pounds | 5.1 pounds (M8A3), 4.3 pounds (T22) |
| Maximum accurate range | 1,000 yards | 800 yards |
| Approximate penetration of Class A armor | 1.75 inches | 1 inch |
| Penetration of good reinforced concrete | 3 feet | 1 foot |
| Operating temperature range | 0 to 120 °F (−18 to 49 °C) | —10 °F to 105 °F (M8A3), -20 °F to 120 °F (T22) |
| Weight of plane mounting installation | 15 pounds (16 mounts) | 196 pounds (6 rockets total, from 2 M10[16] triple-tube cluster launchers). |
UK and US made an exchange of data on their development before US entered the war.