A desperate alternative?

For a brief period after WWII, until effective guided missiles became available, racks of unguided rockets, to be fired in salvoes, became a popular armament option for bomber interceptors.

The figure above illustrates why air forces were eager to explore rockets as an alternative to guns. The weight of a gun scaled, for all practical purposes, linearly with the amount of energy that it imparted on its projectiles. By the end of WWII the axis power were considering guns of a calibre of 50mm or more as the most effective weapons against heavy bombers, as it was thought that only projectiles of this size could carry sufficient explosive and incendiary content to destroy a heavy bomber with one hit. But some of these weapons weighed half a ton apiece. Worse, while the energy these big guns imparted to a single projectile was impressive, the power output of the guns, i.e. the product of projectile energy and rate of fire, stagnated. The development of revolver and rotary cannon after the war partially addressed that bottleneck, as they were more efficient than linear-action guns, but even so the practical limits of gun technology were being reached.

As bombers became bigger, faster and more solidly built, it was plausible that bigger and bigger warheads would be needed to destroy them. At the same time, interception became more difficult because both bombers and fighters were operating at high supersonic speeds. And at the same time too, the spread of nuclear weapons greatly increased the need for effective interception. This confluence of pain factors created a desperate situation, which called for desperate measures. Salvoes of unguided rockets were a plausible answer until guided missiles would become effective.

A long heritage

Rockets were among the first applications of gunpowder, with military uses dating back to the Chinese armies in the 13th century, but their effectiveness appears to have been rather limited until the late 18th century. At that time, the Kingdom of Mysore in southern India started to use rockets with a metal casing, which allowed a larger amount of propellant to be more effectively used, increasing the range and effectiveness of its rockets. In British hands, this design evolved into the Congreve rocket of the Napoleonic wars, introduced in the early 19th century. Made in various sizes, this consisted of a warhead with an explosive or incendiary filing, a combustion chamber with gunpowder propellant, and a long wooden stick attached to the side of the projectile, which served as a primitive tail. The Congreve rocket was inferior in range or accuracy to the smoothbore cannon of the era, but it did provide its users with relatively lightweight and portable firepower, suitable for area bombardment of soft targets.

The Congreve rocket was not the final point of 19th century rocket design, but as it happens, a rather similar weapon was introduced as aircraft armament during the First World War. The Le Prieur system was intended as a weapon against German observation balloons, Drachen, which were large static targets but not easy to bring down as small holes in the balloon envelope did not affect it much, and the balloons were well defended by anti-aircraft guns. The rocket itself was small and made from cardboard with a sharp metal tip. The interwing struts of a biplane fighter were fitted with guidance tubes for the long tail sticks of the Le Prieur rocket, arranged at a positive angle of 17 degrees to the line of flight. The pilots were instructed to approach the elongated German balloon along its length and upwind, in a steep dive of 45 degrees or more. The pilot had to approach the target until it entirely filled the sight, a distance of only 120m, before launching the rockets using their electrical ignition system, and then still press on for a few seconds more, as they took some time to launch. Firing at the closest acceptable range was essential as the weapon was very inaccurate.

A Nieuport 17 in 1916 with launch tubes for Le Prieur rockets installed. The rockets themselves are not present in this picture. (WikiMedia)

Electrical ignition apart, there was little about this weapon that would have surprised Napoleon I. And while the Le Prieur rocket was reasonably effective against static balloons and also used to attack ground targets, it was not considered a suitable weapon against Zeppelins. The British Admiralty (responsible for home defence) evaluated it in 1916, but the performance penalty of 6-7 knots (11-13 km/h) on a Sopwith Baby was considered too much. The weapon was not formally discarded until the next year. The tactical problem was that the attacker would need to be above the target, but Zeppelins could fly higher than most WWI fighters.

The Second World War

The 1930s saw a renewed interest in rocket propulsion everywhere, which included a revival in the development of simple rockets as an aircraft weapon.

In France, experiments with basic black-powder rockets for air-to-ground attack in 1937 revealed a need for improved accuracy, as dispersion was about 20 m at 1000 m range. The development of a better rocket was still ongoing in 1940.

USSR

Some of the most successful work was done in the USSR. Development work on solid propellant rockets had been going on since 1928, but in 1933 the state decided to centralise work on rocket and jet propulsion in a new institute, the RNII, headed by I.T. Klimenov. One of the tasks undertaken by it, under the leadership of G.E. Langemak, was the development of “rocket propelled shells.” There would be two versions, the RS-82 and the RS-132, with the designation indicating their diameter. With an order for 5000 of each placed in 1935, work progressed apace, and the RS-82 and RS-132 rockets were formally accepted for service in 1937 and 1938 respectively, despite the arrest and later the execution of both Klimenov and Langemak, victims of Stalin’s purges.

The RS-82 first saw combat in 1939 in the brief border conflict between the USSR and Japan. It was intended for both air-to-air and air-to-ground use, with a different fuse (AGDT or GVMZ) installed. It was a compact weapon, 622mm long with a weight of between 6.82 and 8 kg depending on the model, and a warhead of 450 to 640 gram. It was launched from underwing rails, which could be installed on fighters, but were widely used on the Il-2 Shturmovik. The nominal range was 5500 – 6200 m, but the speed of the rocket was only 513 m/s, which implies a more curved trajectory than most guns, and even at short range the accuracy left much to be desired. But it was a weapon that could be carried by most aircraft, that could be cheaply mass-produced, and that was effective enough when it hit.

The RS-82 would become very widely used as an air-ground weapon. Both the 82mm and the 132mm rockets would also have widely used ground-to-ground derivatives used by the famous Soviet “Katyushka” rocket launchers, the BM-8 and BM-13.

Bibliography

• The Air Defence of Britain 1914-1918
  Christopher Cole and E.F. Cheesman
  Putnam, 1984
  ISBN 0-370-30538-8
• Nieuport 1909-1950
  Léonard Rosenthal, Alain Marchand, Michel Borget, Michel Bénichou
  Editions Lariviere, Docavia 38
• Les Chtourmovik
  Herbert Léonard
  Editions Lariviere, 1999
  ISBN 2-90705-1-261
• Fighting Techniques of the Napoleonic Age
  Robert B. Bruce, Iain Dickeu, Kevin Kiley, Michael F. Pavkovic, Frederick C. Schneid
  Amber books, 2008
  ISBN 978-1-905704-82-8