The RP-3 (from Rocket Projectile 3 inch) was a British air-to-ground rocket projectile introduced during the Second World War. The "3 inch" designation referred to the nominal diameter of the rocket motor tube. The use of a warhead gave rise to the alternative name of the "60-pound rocket". Though an air-to-ground weapon, it saw limited use in other roles. They were generally used by British fighter-bomber aircraft against targets such as tanks, trains, motor transport and buildings, as well as by Coastal Command and Royal Navy aircraft against U-boats and ships.
Use continued post-war, with the last known major operational use being during the Aden Emergency in 1964, where Hawker Hunters flew 642 sorties and fired 2,508 RP-3s in support of Radforce. Use continued until the withdrawal from Aden Protectorate in November 1967, at which point the RP-3 was withdrawn from service in favour of the newer SNEB. Concerned about the possibility of shipboard radar setting off the SNEB's electrical ignition, the Royal Navy replaced their RP-3s with a new design, sometimes known as the 2-inch RP.
History Earlier systems The first use of rockets fired from aircraft was during the First World War. The "unrotated projectiles" (UPs) were Le Prieur rockets mounted on the interplane struts of Nieuport fighters. These were used to attack observation balloons and were reasonably successful. Sopwith Baby, Sopwith Pup and Home Defence B.E.2 fighters also carried rockets.Aeroplane Monthly June 1995
Development Starting in 1935, the British began development of new anti-aircraft weapons, including cordite-powered surface-to-air rockets. Several models of these Unrotated Projectile (UPs) were introduced, starting with a diameter model that saw use both in ground batteries and on larger ships. In 1937, new models at and diameters were introduced. By 1938, work on the 2-inch model had been slowed in favour of the 3-inch models which offered performance similar to the QF 3-inch 20 cwt anti-aircraft gun. Tests in Bermuda in 1939 suggested that the accuracy was not high enough to be used in a fashion similar to a gun, and development was slowed.
After the Dunkirk evacuation in 1940 it was clear an attack on the UK was coming, and production was quickly ramped up. Still considering the accuracy to be low, they were to be fired in salvos from the "Z-Batteries". Consisting largely of light metal tubes on a rotating platform, 7,000 launchers were available by August 1940, although production of the rockets themselves lagged and only 10 rockets each were assigned to 840 launchers. Several updated models of the launchers were introduced and the system claimed a small number of aircraft.
Air-to-ground When German forces under the command of Erwin Rommel intervened in the Western Desert campaign from early 1941, it became clear that the Desert Air Force lacked weapons capable of damaging or destroying the large numbers of armoured fighting vehicles, particularly the heavier Panzer III and Panzer IV medium tanks used by the Germans. In April 1941 Henry Tizard, the chief scientist of the British government, called together a panel to study "Methods of Attacking Armoured Vehicles".
The types of weapons investigated included the 40 mm Vickers S gun and related weapons manufactured by the Coventry Ordnance Works, as well as the Bofors 40 mm and the US 37 mm T9 cannon fitted to the Bell P-39 Airacobra; it was already recognised that these weapons were only capable of dealing with light tanks and motor transport. Using larger weapons on fighter-bombers was ruled out because of weight and difficulties handling recoil. The chairman of the panel, Mr. Ivor Bowen (Assistant Director of Armament Research) turned to the idea of using rocket projectiles to deliver a large warhead capable of destroying or disabling heavy tanks. Information was sought from the Soviets, who had been using unguided RS-82 rockets since 1937.The possibility of the Soviets sending a team of engineers to help set up production of these weapons was canvassed in August 1941. The Soviet offer was withdrawn, in spite of Operation Benedict British efforts at supplying Hawker Hurricanes and training Soviet aircrew in their use.
By September 1941 it was decided that two models of UP would be developed: A 23 lb plastic explosive on a standard 2-inch UP A 20 lb solid armour-piercing head on a 3-inch UP
When it was realised that the 2-inch version would be less effective than the Vickers S cannon, it was decided to concentrate on development of the 3-inch version, which could be developed from the 3-inch rocket used in the Z-Batteries.
Design
The rocket body was a steel tube in diameter and longAP2802 Section 3 Chapter 2, paragraph 5 filled with of cordite propellant, fired electrically.Bestämmelser för rakettjänst, p2 The warhead was screwed into the forward end, and was initially a solid , diameter and long (with adaptor)AP2802 Section 3 Chapter 3, paragraph 4 armour-piercing warhead which was quickly supplanted by a , high explosive head. For practice there were also a mild steel semi-armour-piercing warhead, a concrete practice head and a concrete practice head. Once the rocket had been mounted on the rails, an electrical lead (or "pigtail") connected the rocket to the firing controls.
Four large tailfins AP2802 Section 3 Chapter 2, paragraph 14 induced enough spin to stabilize the rocket, but as it was unguided, aiming was a matter of judgment and experience. Approach to the target needed to be precise, with no sideslip or yaw, which could throw the RP off line. Aircraft speed had to be precise at the moment of launch, and the angle of attack required precision. Trajectory drop was also a problem, especially at longer ranges.In tests carried out by the A&AEE, dispersion (when aimed at a square target) was at range – equal to 3° to 4° aiming error.Aeroplane Monthly July 1995
The rocket was less complicated and more reliable than a gun firing a shell and there was no recoil on firing. It was found to be a demoralising form of attack against ground troops and the 60-pound warhead could be devastating. The rocket installations were light enough to be carried by single-seat fighters, giving them the punch of a cruiser.A typical Royal Navy cruiser of the era carried eight to twelve 6-inch guns firing projectiles, while a fighter could fire eight 60-pound RP-3 rockets in a single salvo. Against slow-moving large targets like shipping and U-boats, the rocket was a formidable weapon.
The weight and drag of the all-steel rails initially fitted to British aircraft blunted performance. Some aircraft such as the Fairey Swordfish biplane used against submarines had steel "anti-blast" panels fitted under the rails to protect the wing, which further increased weight and drag. Aluminium Mark III rails, introduced from late 1944, reduced the effect. American experience with their own rockets (the USAAF's 3.5-Inch Forward Firing Aircraft Rocket (FFAR) and the US Navy's 5-inch FFAR and HVAR3.5 in FFAR 5 in FFAR and HVAR Retrieved 6 March 2008) showed that the long rails and anti-blast panels were unnecessary; zero-length launchers were introduced in May 1945. British aircraft started being fitted with "zero-point" mounting pylons in the post-war years.
The 3-inch rocket motors (less warhead) were used in the 'bunker buster' "Disney bomb" (official name: 4500 lb Concrete Piercing/Rocket Assisted bomb), 19 of them propelling the bomb to at impact with the target.
Service history Air-to-ground use
Before the new weapon was released for service extensive tests were carried out by the Instrument, Armament and Defence Flight (IADF) at the Royal Aircraft Establishment, Farnborough. Hawker Hurricanes were fitted with rockets and rails and flown during June and July 1942. Further tests were undertaken from 28 September to 30 November to develop rocket-firing tactics. Other aircraft used were a Lockheed Hudson, a Fairey Swordfish biplane torpedo bomber, a Douglas Boston medium bomber and a Sea Hurricane. At the same time the Aeroplane and Armament Experimental Establishment (A&AEE) had to develop tactics for all the individual aircraft types which were to be armed with the RPs. Aiming was through a standard GM.II reflector gunsight. A later modification enabled the reflector to be tilted with the aid of a graduated scale, depressing the line of sight, the GM.IIL. For rockets only the Mk IIIA was the most successful – it was used on the Lockheed Ventura and Hudson.
The first operational use of the RP was in the Western Desert campaign as a "tank-busting" weapon on Hawker Hurricane Mk. IIEs and IVs. The 25-pound armour-piercing heads were found to be ineffective against the Tiger I heavy tanks coming into German service. With the example of the success of Royal Artillery gunners using high-explosive shells from their Ordnance QF 25 pounder gun-howitzers, it was decided to design a new 60-pound semi-armour-piercing (SAP) head. These were capable of knocking turrets off tanks.Hills 2003, page 121
A typical RP-3 installation was four projectiles on launching rails under each wing. A selector switch was fitted to allow the pilot to fire them singly (later omitted), in pairs, or as a full salvo. Towards the end of the war some RAF Second Tactical Air Force (2 TAF) Hawker Typhoons had their installation adapted to carry an additional four rockets doubled up under the eight already fitted.Shores & Thomas 2005, pages 245-250
RP-3s were widely used during the battle the Falaise pocket in mid-August 1944. During the battle German forces, retreating to avoid being trapped in a pincer movement by Allied ground forces, came under air attack. Amongst the waves of light, medium and fighter bombers attacking the German columns the Typhoons of 2 TAF attacked with their rockets, claiming hundreds of tanks and "mechanised enemy transport".also known as "motorized enemy transport", as opposed to "horse-drawn transport" (HDT) After the battle, Army and 2nd TAF Operational Research Sections studying the battleground came to the conclusion that far fewer vehicles, 17 in total, had been destroyed by rocket strike alone. What was clear was that in the heat of battle it was far harder for pilots to launch the weapons while meeting the conditions needed for accuracy. Smoke, dust and debris in the target areas made accurate assessment of the damage caused almost impossible. It was also clear that rocket attacks devastated the morale of enemy troops – many vehicles were found abandoned intact, or with only superficial damage. Interrogation of captured prisoners showed that even the prospect of rocket attack was extremely unnerving for them.
Large stocks of RP-3s remained at the end of the war and they were used well into the jet age. They were used operationally during the Malayan Emergency, Korean War and the Indonesia–Malaysia confrontation. The last known use in combat is by Hawker Hunters in Aden from 1964 to as late as 1967 in support of Radforce. When these aircraft moved to Bahrain in November 1967, the remaining RP-3s were withdrawn from service and replaced by the newer SNEB.
Anti-submarine
Soon after some encouraging results from the initial deployment, trials of the weapon were conducted against targets representing U-boats. It was discovered that if the rockets were fired at a shallow angle, near misses resulted in the rockets curving upwards in seawater and piercing the targets below the waterline. Soon Coastal Command and the Royal Navy's Fleet Air Arm aircraft were using the rockets extensively.