The Unrotated Projectile (UP) was a British anti-aircraft and ground-bombardment rocket of the Second World War. The original 7-inch version was developed for the Royal Navy by Alwyn Crow of the Projectile Development Establishment of the Ministry of Supply at Fort Halstead. These were generally similar in layout to contemporary mortar bombs. It proved unreliable and ineffective and was withdrawn from use in 1941.
Further development of the concept led to the UP-2 and UP-3, which had diameters of 2-inch and 3-inch respectively and were longer. The UP-3 was used as the basis of the Z Battery anti-aircraft weapons and later developed in air-to-ground form as the RP-3, used against ground forces and shipping by aircraft like the Typhoon and the Beaufighter. In 1944–1945 several adaptations for general bombardment were produced, including Sea Mattress, Land Mattress, LILO and Tulip.
Development
Awareness of French and German rocket research in the early 30s coincided with rearmament from 1934. By 1935, the Research Department had set up specialist branches in the Ballistics Directorate and the Explosives Directorate to look into the use of rockets against aircraft. To a lesser extent, the researchers looked into long-range rocketry as a replacement for pilotless aircraft and use as a take-off aid for heavily laden aircraft. The Ballistics Directorate designed components and studied ballistics theory, prediction and stability. The Explosives Directorate worked on a propellant which burnt at a "steady controllable pressure; whose surface, during burning, will remain constant and which will leave, at the end of the burning, as little un-burnt residue as possible". The research threw up more problems; the charges had to be packed in non-inflammable material and a substance had to be developed that was impervious to rapid acceleration and differential gas pressure.
The acceleration of a rocket was far slower than that of projectiles which meant that a new type of fuze, not reliant on acceleration to be armed, was necessary. The cordite propellant had to be formed in unusual shapes which made extrusion a much more elaborate process but by 1936, the Director of Ballistics Research, Alwyn Crow reported that the rockets should be considered as practical weapons of war. A new propellant, solvent-less cordite (Cordite SC) was invented. In July 1936, Crow took over a new Projectile Development Establishment at Fort Halstead which was overseen by the Sub-Committee on Air Defence Research of the Committee of Imperial Defence. In November 1939, Winston Churchill as First Lord of the Admiralty asked Crow urgently to design a means of laying an aerial minefield and to consider other methods of protecting ships against aircraft. Frederick Lindemann, the chief scientific advisor to the government, had previously advocated a scheme for "dropping bombs hanging by wires in the path of attacking aircraft".
In October 1937, the Sub-Committee on Air Defence decided that the 3-inch rocket would take precedence over the 2-inch projectile and that the policy would be to obtain a rocket which, though not ideal, would be a practical weapon. Work on the 2-inch rocket was set aside for the 3-inch version which was comparable to the ammunition fired by the QF 3-inch 20 cwt and QF 3.7-inch anti-aircraft guns against aircraft at medium and high altitudes. By the end of 1938, trials of components were complete (except for the fuze) and proposals for twin and quadruple projectors were solicited from Vickers-Armstrongs. An advantage of a rocket weapon was that it did not need to be produced by traditional armaments firms, except for the novel Cordite SC which would need new facilities at Royal Ordnance Factories. The term unrotated projectile was used as a cover name to disguise the use of a rocket system; the projectile was not spin-stabilised (except for later examples used for land bombardment later in the war).
On 14 November 1939, in his first numbered memo as First Lord of the Admiralty, Winston Churchill, requested weekly reports on the rocket development programme. Churchill wanted plans be made to fit four projectors apiece on five battleships, a pair each onto six cruisers and one on the monitor under the impression that the rocket armament would make the ships invulnerable to air attack. By April 1940, about forty projectors were ready, firing a container for a parachute, cable and a bomb or a mine, intended to drift into the paths of attacking aircraft. The first operational use of rockets by any country took place in July 1940.
Variants
2-inch rocket
The 2-inch rocket was superseded by the 3-inch version but work continued at a reduced tempo. The device contained a stick of Cordite SC with electrical ignition. Fuze 720, a wind-vane armed impact fuze, with a self-destruct timing device set for 4.5 seconds, at an altitude of about . The rocket was fired after the motor had been ignited for 0.1 second and burned for 1.2 seconds. Without the self-destruct mechanism, the rocket could reach .
Several launcher types were designed for naval use to defend merchant ships and as a means of illumination but only the Mk II (also known as the Pillar Box mount) was used on land at sites on the south coast. A cabin housed the operator with ten rocket launchers on each side, from which the HE rockets could be fired in salvoes of ten or all at once by the use of foot pedals to trigger electric ignition. The Pillar Box had 360° traverse and elevation of 0° to +85°.
3-inch rocket
The Admiralty was more interested in the rocket concept but the War Office took the view that rockets would be useful for area bombardment and envisaged 285 rocket units with four quadruple launchers apiece and sixty launchers in reserve, which might also allow the QF 3-inch 20 cwt guns to be put in reserve, ready to equip new units raised if war came. The Army waited on trials of the rockets conducted in Jamaica in early 1939, which were judged to be satisfactory and the Sub-Committee on air Defence Research recommended that the 3-inch UP be taken into service. The decision was postponed because the Director of Artillery judged the rocket lacked the accuracy for medium and high altitude fire.
The rocket project languished until the Dunkirk evacuation in June 1940. It was assumed that the rocket lacked the accuracy of gunfire but this assumed that accuracy was necessary. There was a paradox in trying to predict the position of an aircraft in time and space when the direction, height and speed of an aeroplane were inherently unpredictable. It had not been possible to test conventional anti-aircraft fire under wartime conditions, to calculate a statistical norm for the number of shells needed to shoot down a aircraft. It had been assumed that the 3-inch rocket would have a less stable trajectory and that this would make prediction more difficult; this did not take account of the larger explosive charge carried by the rocket, which needed a much thinner casing than that of a shell and was lethal over a greater volume of space.
The first 3-inch Z Battery was established near Cardiff but the test battery at Aberporth claimed the first German aircraft. Anti-Aircraft Command (AA Command) was allocated 8,000 rocket projectors, of which more than 7,000 were ready by August 1940. Rocket production was well short of the planned output, only 8,400 being provided to AA Command. Priority was awarded to the Admiralty and the quota for AA Command was limited to ten rockets each for 840 projectors.
Projector, 3-inch Mk 1 Rails: Weight (approx.): Height (rails depressed): Width: Elevation: 0°–70° Traverse: 360°
The projector was made by the manufacturing firm G. A. Harvey of Greenwich, which delivered a batch of ten projectors less than six weeks after receiving the drawings. By September, the firm had completed 1,000 launchers from the order for 2,500 as the Mark 1 for the Army and 3-inch Harvey L. S. Projector for the Navy, most of which were fitted to merchant ships. The rocket was fired from two rails; aiming was simple, behind a shield the layer on the right hand side pushed the apparatus in the direction of the target using a crude sighting device and the layer on the left locked the launcher before the rocket was fired using electrical ignition. A test battery was set up at Aberporth and other rocket sites were manned by the Home Guard; many of the Mark 1 projectors were used for tests and training.
Projector, rocket, 3-inch No.2 Mk 1 Rails: Weight: Height (rails up): Width: Length: Elevation: 10°–80° Traverse: 360°
The No.2 Mk 1 was the first projector to be mass-produced and could launch two rockets, both from two rails. A hand wheel elevated the projector, traverse was by hand-crank and the rocket motors were launched by electrical ignition from a battery. The base of the launcher was embedded in concrete or mounted on a No. 2 firing platform. A battery of No. 2 projectors was sent to North Africa and used to defend ports.
Projector, rocket, 3-inch No.4 Mk 1 and 2 Rails (long): Rails (short): Weight: Width: Length: Height (travelling): Height (rails up): Elevation: 7°–75° Traverse: 360°
The No.4 projector was designed for mobile use; nine rockets were mounted on 36 rails, two long and two short for each rocket, in vertical banks. The only difference between marks was that the Mk 2 had an electro-magnetic fuze setter. The two operators were housed in two metal cabins, either side of the banks of rockets one traversing and the other elevating the launcher. The rockets could be fired in .75 seconds or in four salvoes of 3, 2, 2 and 2. For movement, the first launchers were carried on an adapted 3-inch anti-aircraft gun platform. The No.2 Mk 1 platform was derived from the Mk 3A 3-inch AA platform, No. 2 Mk 1A was adapted from the Mark 3B platform, No.4 MK 1B rode on the Mk 4A and the Mk 1C was mounted on the Mk IVA platform. A hundred were built, comprising eight batteries, two of which were sent to North Africa.
Projector, rocket, 3-inch No.6 Mk 1 Rails: Weight: Width: Width (cabin): Length (at 20°): Length (at 80°): Height (at 20°): Height (at 80°): Elevation: 20°–80° Traverse: 345°
The No.6 projector was the largest variant and was another static equipment, going into service in 1944. Twenty rail sets in two banks of ten rail sets, either side of a two-man cabin, fired twenty rockets in .75 seconds or salvoes of 6, 4, 6 and 4. A 7.2-volt battery provided the ignition, operated by a foot-pedal. The elevator sat at the front with a window with simple sights and the traverser sat behind him, also with sights and a window in the cabin roof; both men were in contact with a command post.
Projector, rocket, 3-inch, No.8 Mk 1 (Land Mattress)
Length (barrel): Weight (unloaded): Weight (loaded): Length: Height (travelling): Wheel track: Elevation: 23°–45° Traverse: 20° Projectile spin: 660 rpm
Work on a 5-inch artillery rocket was unsatisfactory because of dispersion and short range but the device was adopted by the navy as a shore bombardment weapon. A Landing Craft Tank (Rocket) carried 180 sextuple army launchers (1,080 rockets) with a range and known as Mattress. More research showed that a slight rotation increased the accuracy of a fin-stabilised rocket, which was tried with an RP-3 No. 1 rocket motor and a navy warhead. Range increased to but the Mattress for the Land rocket was limited in elevation from +23° to +45° which restricted the minimum range to . For shorter-range fire, a spoiler was fitted over the rocket exhaust which could be part-closed, limiting the exhaustion of the gases. Three spoilers were made, which could shorten the range in stages to . The motor consisted of a cruciform stick of Cordite SC which burned for 1.6 seconds and a new 3-inch warhead was developed but this was not used.
Land Mattress projector