RP-3

The RP-3 (from Rocket Projectile 3 inch), was a British air to ground rocket used in the Second World War. The use of a 60 lb (27 kg) warhead gave it the alternative name of the "60 lb rocket"; the 25 lb (11.3 kg) solid-shot armour piercing variant being 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.

History

The first use of rockets fired from aircraft was during World War One. 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 Babies and Pups and Home Defence B.E. 2s also carried rockets.Aeroplane Monthly June 1995] With the end of the War the Royal Air Force, intent on retrenching, forgot about the potential uses for rockets fired 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.The Blitz Then and Now: Volume 3]

When German forces under the command of Rommel intervened in the Western Desert from early 1941 it became clear that the Desert Air Force did not have the 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. Something needed to be done and 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 Bofors and the 37 mm T9 cannon fitted to the 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 Russians who had just started using unguided RS-82 rockets against German ground forces in the opening phases of Operation Barbarossa. [Note: The possibility of the Russians sending a team of engineers to help set up production of these weapons was a possibility in August 1941. However the Russian offer was withdrawn, in spite of British efforts at supplying a Wing of Hawker Hurricanes and training Russian aircrew in their use.]

By September 1941 it was decided that two models of UP (Unrotated Projectiles) would be developed:
* A 23 pound 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 in version which could be developed from the 2 inch rocket used in the Z-Batteries.

Design

The rocket body was a steel tube 3 inches (76 mm) in diameter, hence the name. The tube was filled with 11 pounds (5 kg) of cordite which was the propellant; this was fired electrically. A warhead was screwed into the forward end, initially a solid 25 lb (11 kg), 3.44 inch armour piercing shell which was quickly supplemented by a 6 in diameter, 60 lb (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 (nicknamed "pigtail") was plugged into the exhaust of the rocket.

Four small tailfins were fitted which gave enough spin to stabilize the rocket, though it was unguided and targeting was a matter of judgment and experience. For a start the approach to the target needed to be precise, with no sideslip or yaw which could throw the RP off line. Aircraft speed also had to be precise at the moment of launch and, because the launch rails were a fixture, the angle of attack also required precision. Trajectory drop was also a problem, especially at longer ranges. [Note: 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.] Aeroplane Monthly July 1995] .

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. Against slow-moving large targets like shipping and U-boats the rocket was a formidable weapon.

Unfortunately the weight and drag of the all-steel rails as initially fitted to British aircraft had a detrimental effect on the aircraft's 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 FFAR (Folding Fin Aircraft Rocket) and the USN's 5-inch FFAR & HVAR [ [http://www.designation-systems.net/dusrm/app4/35in-rockets.html 3.5 in FFAR] [http://www.designation-systems.net/dusrm/app4/5in-rockets.html 5 in FFAR and HVAR] Retrieved 6 March 2008] ) showed that the long rails and anti-blast panels were unnecessary. British aircraft only started being fitted with "Zero-Point" mounting pylons in the post-war years

Use in battle

Air to Ground Use

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 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 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. [ [http://www.429sqn.ca/acmgs.htm GM.IIL] ]

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 Panzer VI "Tiger" tanks coming into service. With the example of the success Royal Artillery gunners were getting 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.

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 Royal Navy aircraft were using the rockets extensively. The first U-Boat destroyed with the assistance of a rocket attack was U-752 (Kāpitan-Leutnant Schroeter) on May 23 1943 by a Swordfish of 819 NAS. One rocket punched right through the pressure hull, rendering the U-Boat unable to dive: U-752 was scuttled by the crew. On May 28 1943 a 608 Squadron Hudson destroyed a U-Boat in the Mediterranean, the first destroyed solely by rocket.

From then until the end of the Second World War in Europe, Coastal Command and the Fleet Air Arm would use the rockets as one of their primary weapons (alongside torpedoes, which, to a certain extent they replaced) against shipping and surfaced U-Boats.

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.Shores and Thomas 2005, pages 245-250]

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". However, 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 actual damage caused almost impossible.

However, it was also clear that the rocket attacks were devastating to the morale of the enemy troops: many vehicles were abandoned intact or with superficial damage and interrogation of captured prisoners showed that even the prospect of rocket attack was extremely nerve racking.

Tank Use

In 1945, some British Sherman tanks were fitted with two rails, one either side of the turret, to carry two 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 Fireflys.

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. cite book | last = Fletcher | first = David | title= Sherman Firefly | date=2008 | publisher= Osprey Publishing | id = ISBN 1846032776] .

pecification

*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

*Warhead
**"60 lb Shell, HE/SAP" (Semi-armour piercing)(27 kg)
**"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) (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 War

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 Forces

* 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.)
* Vickers Wellington GR Mk. XIV: (Coastal Command)

Royal Navy Fleet Air Arm

* Fairey Firefly Mk. I
* Fairey Swordfish Mk. II, III
* Grumman Tarpon/Avenger Mk. I, II, III

References

;Bibliography
* 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.

ee also

*Land Mattress
*Cap Arcona