The RP-3 (from Rocket Projectile 3 inch) was a British rocket projectile used during and after the Second World War. Though primarily an air-to-ground weapon, it saw limited use in other roles. Its 60 lb (27 kg ) warhead gave rise to the alternative name of the "60 lb rocket"; the 25 lb (11.3 kg) solid-shot armour-piercing variant was referred to as the "25 lb rocket". They were generally used by British fighter-bomber aircraft against targets such as tanks, trains, motor transport and buildings, and by Coastal Command and Royal Navy aircraft against U-boats and shipping. The "3 inch" designation referred to the diameter of the rocket motor tube.
Loading 3in 60-pdr SAP/HE rocket projectiles onto a Hawker Typhoon
|Type||Unguided air-to-surface rocket|
|Place of origin||United Kingdom|
|Used by||Royal Air Force, Royal Navy, Royal Australian Air Force|
|Wars||World War II|
|Mass||82 pounds (37 kg)|
|Length||55 inches (140 cm)|
|Diameter||3 in (76 mm) rocket body|
|Warhead||12 lb (5.4 kg) High explosive (TNT or TN/RDX) when used|
|Warhead weight||60 lb (27 kg)|
|Engine||Solid fuel rocket|
|1,700 yards (1,600 m)|
|Speed||1,600 feet per second (480 m/s)|
|Aircraft, Sherman Tulip, LCT (R)|
The first use of rockets fired from aircraft was during World War I. The "Unrotated Projectiles" were Le Prieur rockets which were mounted on the interplane struts of Nieuport fighters. These were used to attack observation balloons and were reasonably successful. Sopwith Baby and Pup and Home Defence B.E.2 fighters also carried rockets. With the war ended the Royal Air Force, intent on retrenching, forgot about firing rockets from aircraft. The British Army, however, did see a use for rockets against low-flying aircraft; from late 1940 parts of Britain were defended by increasing numbers of "Z-Batteries" 2-inch (51 mm) rockets supplementing the conventional anti-aircraft guns.
When German forces under the command of Rommel intervened in the Western Desert 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 tanks possessed by the Germans. Consequently, in April 1941 Henry Tizard, the Chief Scientist, 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 40mm Bofors and the US 37 mm T9 cannon fitted to the Bell P-39 Airacobra: however, it was already recognised that these weapons were only capable of dealing with light tanks and motor transport, and 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 as a means of delivering a large warhead capable of destroying or disabling heavy tanks. Information was sought from the Soviets, who had just started using unguided RS-82 rockets against German ground forces in the opening phases of Operation Barbarossa.[note 1]
By September 1941 it was decided that two models of UP (Unrotated Projectiles) would be developed:
- A 23 lb plastic explosive on a standard 2-inch (51 mm) UP.
- A 20 lb solid armour-piercing head on a 3-inch (76 mm) 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 2-inch rocket used in the Z-Batteries.
The rocket body was a steel tube 3 inches (76 mm) in diameter filled with 11 pounds (5 kg) of cordite propellant, fired electrically. The warhead was screwed into the forward end, and was initially a solid 25 pounds (11 kg), 3.44-inch (87 mm) armor-piercing shell which was quickly supplemented by a 6-inch-diameter (152mm), 60 pounds (27 kg) high-explosive head. Another type of head was a 25 lb (11 kg) mild steel (later concrete) practice head. Once the rocket had been mounted on the rails, an electrical lead (or "pigtail") was plugged into the exhaust of the rocket.
Four large tailfins 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.[note 2]
On the plus side 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 lb warhead could be devastating. The rocket installations were light enough to be carried by single-seat fighters, giving them the punch of a cruiser.[note 3] 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 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 USN's 5-inch FFAR & HVAR) 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, 19 of them propelling the 4,500 pounds (2,000 kg) bomb to 990 miles per hour (1,590 km/h) at impact with the target.
Use in battleEdit
Before the new weapon was released for service extensive tests were carried out by the Instrument, Armament and Defence Flight (I.A.D.F) at Royal Aircraft Establishment, Farnborough. 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 Hudson, a Swordfish, a Boston II 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 Ventura and Hudson.
The first operational use of the RP was in the Western Desert as a "tank-busting" weapon on Hawker Hurricane Mk. IIEs and IVs. The 25 lb armour-piercing heads were found to be ineffective against the Tiger I tanks coming into German service. With the example of the success of Royal Artillery gunners using high-explosive shells from the 25 pdr gun-howitzer, it was decided to design a new 60-pound semi-armour-piercing (SAP) head. These were capable of knocking turrets off tanks.
A typical RP-3 installation was 4 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 Hawker Typhoons had their installation adapted to carry an additional four rockets doubled up under the eight already fitted.
Possibly the best known action involving RP-3s was that of the Falaise pocket of 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".[note 4] 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.
But it was also clear 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.
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.
The first U-Boat destroyed with the assistance of a rocket attack was U-752 (Kapitän-Leutnant Schroeter), on 23 May 1943, by a Swordfish of 819 NAS. The rockets used on this occasion had solid, cast-iron heads and were known as Rocket Spears. One of these punched right through the submarine's pressure hull and rendered it incapable of diving; the U–boat was scuttled by its crew. On 28 May 1943, a 608 Squadron Hudson destroyed a U-boat in the Mediterranean, the first destroyed solely by rocket. These rockets were, among other factors, credited with making it too dangerous for the Germans to continue operating their Flak U-Boats, which were initially designed with heavy anti-aircraft weaponry to hold off air attacks.
From then until the end of the Second World War in Europe, Coastal Command and the Fleet Air Arm used the rockets as one of their primary weapons (alongside torpedoes, which, to a certain extent they replaced) against shipping and surfaced U-Boats.
In 1945, some British Shermans were fitted with two or four rails – one or two either side of the turret – to carry 60 lb (27 kg) headed rockets. These were used at the Rhine Crossing by tanks of the 1st Coldstream Guards. The tanks were called "Sherman Tulips". The tanks fitted included both conventional Shermans and the more heavily armed Sherman Fireflies.
The modifications were first tried out by two officers of the 1st Armoured Battalion, Coldstream Guards, 5th Guards Armoured Brigade, who obtained rockets and launching rails from an RAF base and carried out the first test firings on 17 March 1945. They were inspired after hearing the idea had been earlier tried, but abandoned, by a Canadian unit, the 12th Manitoba Dragoons, who had fitted RP-3 rails to a Staghound Armoured Car.
Within a week all the tanks of Number 2 Squadron had been fitted with launch rails, some tanks had two launching rails, others had four. The rails were at fixed elevations and the rockets had fixed ranges either 400 or 800 yards (370 or 730 m).
The rockets were highly inaccurate when fired from a tank as they were being fired from a stationary point and had little slipstream over the fins. Despite this, the RP-3 was valued by tank crews for the destructive effect of its 60-pound warhead. In combat, they were also used for short-range, saturation bombardment of an area and were effective as an immediate counter to German ambushes.
- Length: 55 in (1.4 metres)
- Propelling charge: 11 lb (5 kg) cordite, electrically ignited.
- Max speed 1,200 mph (480 m/s)
- Range: 1-mile (1,600 m)
- Weight: 47 lb (21 kg) with 25 lb (11 kg) AP head
Names referred to complete weight of the warhead fitted to the rocket body.
- 60 lb Shell, HE/SAP "Semi-armour-piercing" with 12 lb (5.4 kg) TNT filling
- 60 lb Shell, HE/GP, Hollow charge
- 18 lb Shell, HE – (8 kg)
- 25 lb Shot, AP – (11 kg)
- 25 lb Head, Solid, A/S – anti-submarine use (11 kg)
- 60 lb Shell, Practice – training only (27 kg)
- 12 lb Head, Practice – training only (5 kg)
Aircraft using the RP-3 in the Second World WarEdit
These are aircraft that used the RP-3 operationally, a number of aircraft types were fitted with RP-3s on an experimental basis.
RAF and Commonwealth Air ForcesEdit
- Boeing Fortress Mk. II and IIA: (Coastal Command)
- Bristol Beaufighter Mk. VI, VIC, X and 20: (Coastal Command, South East Asia Command and Royal Australian Air Force, Pacific Theatre.)
- Consolidated Liberator B. Mk. III, VI: (Coastal Command.)
- de Havilland Mosquito F.B. Mk. VI: (Coastal Command, SEAC and RAAF, Pacific Theatre.)
- Hawker Hurricane Mk. IIE & IV: (DAF, 2 TAF, SEAC.)
- Hawker Typhoon Mk. Ib: (2 TAF.)
- Republic Thunderbolt (USAAF used their M8 for this role instead, 6/aircraft)
- Vickers Wellington GR Mk. XIV: (Coastal Command)
- Aircraft types included:
- Royal Navy: Hawker Sea Fury and Sea Hawk; Supermarine Attacker and Scimitar;
- RAF: Bristol Brigand, de Havilland Hornet, de Havilland Vampire and de Havilland Venom, Gloster Meteor, and the Hawker Hunter.
- Operational use included the Malayan emergency, the Korean War, the Suez crisis, and the Radfan campaign.
- The possibility of the Soviets sending a team of engineers to help set up production of these weapons was a possibility in August 1941. However, the Soviet offer was withdrawn, in spite of British efforts at supplying a Wing of Hawker Hurricanes and training Soviet aircrew in their use.
- In tests carried out by the A&AEE, dispersion (when aimed at a 20 ft square (1.858 sq m) target) was 13 ft 6 in (4.1 m) at 1,000 ft (305 m) range – equal to 3-4 degrees aiming error.
- A typical cruiser gun of the era, the 6" gun used on Royal Navy ships for instance, fired perhaps 4 or 6 112lb projectiles, while a fighter could fire 8 60lb PR-3 in a single salvo.
- also known as "Motorized Enemy Transport", as opposed to HDT – "Horse Drawn Transport"
- Aeroplane Monthly June 1995
- The Blitz Then and Now: Volume 3
- Aeroplane Monthly July 1995
- 3.5 in FFAR5 in FFAR and HVAR Retrieved 6 March 2008
- Burakowski, Tadeusz; Sala, Aleksander (1960). Rakiety i pociski kierowane [Rockets and guided missiles] (in Polish). Część 1 – Zastosowania (Volume 1 – applications). Warsaw: Wydawnictwo Ministerstwa Obrony Narodowej (Ministry Of National Defense Publishing House). pp. 556–557.
- GM.IIL 429sqn.ca
- Shores and Thomas 2005, pages 245-250
- Gerald Pawle, The Wheezers & Dodgers, Seaforth Publishing 2009 ISBN 978-1-84832-026-0[page needed]
- Moore, Craig (April 28, 2016). "Sherman Tulip Rocket Firing Tanks". www.tanks-encyclopedia.com.
- Fletcher, David (2008). Sherman Firefly. Osprey Publishing. ISBN 1-84603-277-6.
- Ramsay, Winston (editor). The Blitz Then and Now; Volume 3. London, UK: Battle of Britain Prints International Limited, 1990. ISBN 0-900913-58-4
- Shores, Christopher and Thomas, Chris. Second Tactical Air Force Volume Two. Breakout to Bodenplatte July 1944 to January 1945. Hersham, Surrey, UK: Ian Allan Publishing Ltd, 2005. ISBN 1-903223-41-5
- Webb, Derek Collier. "Rocket Attack part 1". Aeroplane Monthly Volume 23, No 6, Issue No 266. June 1995.
- Webb, Derek Collier. "Rocket Attack part 2". Aeroplane Monthly Volume 23, No 7, Issue No 267. July 1995.