CONTAINERS AND PANNIERS
Stores containers and panniers had to meet several criteria. Containers had to be designed to fit into the bomb bay of the aircraft and to be sufficiently robust to withstand the stresses imposed by aircraft manoeuvres and from the impact with the ground. They had to house a parachute at one end and an impact absorbing device at the other. Panniers had to be of a size, shape and weight to enable them to be manhandled around inside the aircraft to the jump hole and their contents so packed as to protect them from impact. During flight they had to be securely anchored to the airframe. Both containers and panniers had to be easily opened and yet secure enough to withstand dropping into the slipstream of the aircraft. Furthermore, they had to be readily removable from the landing site by the minimum of people. The two main types of containers introduced in the early days were the C-type and the H-type.
The C-Type Container
The C-type container adopted by the Airborne Forces consisted of two strengthened sheet metal half-cylinders hinged together along their whole length. The hinged doors were held closed by three quick release catches which were themselves prevented from premature opening by split pins. The container was 5 ft 8 in long and 15 in in diameter and could accommodate either long items such as rifles or Bren guns, or be fitted with three smaller cylinders (15 in diameter by 19 in long) to hold smaller items. These were metal drums fitted with simple quick release lids bedding on to rubber rings and had two carrying handles. Externally, one end of the main container formed a cowling to accommodate the parachute while at the other was an impact absorbing head. In earlier models this was a pad of Sorbo rubber but later it consisted of a metal dome containing a few large cut-outs designed to assist its collapse and hence to absorb the energy of impact. The container was carried in the 500 lb (227 kg) or universal bomb rack by a single suspension lug. In packing the container, care had to be taken to adjust the centre of gravity to within a few inches of a fixed distance from the suspension lug.
They could contain a load of up to 220 lb (100 kg) of stores giving a total weight of 330 lb (150 kg) and were fitted with carrying handles but needed several men to transport them any distance. The preferred drill was to remove the internal cells to give smaller loads for transportation from the DZ and to bury the container and parachute. Alternatively, Reception Committees often arranged for the availability of farm carts or lorries to enable the containers to be removed from the DZ to hidden storage as quickly as possible. Burying or hiding containers was often a problem: to this end at least one container in a drop included a trenching tool.
The H-Type Container
A Polish captain, concerned about the difficulty of burying C-type containers in the hard soil of his country, invented a revised design which became known as the H-type container. It was made up of five interlocking cells held together by long rods with locking levers and safety pins. When these rods were withdrawn each cell could be handled on its own and was therefore easier to remove from the landing site and to conceal. It was two inches shorter than its predecessor, had a payload of 235 lb (107 kg) with the same gross weight of 330 lb (150 kg) and was fitted with straps for ease of handling on landing. One disadvantage was that it could not carry long items. It was, however, capable of delivering a consignment of petrol and oil in three fitted Jerry cans and external clips enabled a trenching tool to be fitted. With the Polish officer supervising the development, the H-type containers were produced by the South Metropolitan Gas Company.3
Panniers
Metal containers were not the only means used for packing and delivering stores. A pannier had been developed consisting of a frame of spring steel wire to which was fitted a mild steel lattice. The pannier was in two parts with one fitting snugly inside the other to form a fully enclosed box shape. Each half was covered with khaki canvas duck. For ease of storage and, more importantly, opening in the field, the side frames could be hinged down until the whole assembly was flat. Four sizes were provided ranging from 22 × 16 × 16 in (560 × 410 × 410 mm) to 29 × 18 × 13 in (740 × 460 × 330 mm) and to protect the contents some were fitted with a coil spring shock-absorbing panel in the base. Normal packing materials used were hairlock panels and layers of Koran fibre needled on canvas.4
Packing of both containers and panniers was an important job. When carried out properly the load could be very secure, as illustrated by the fact that of a consignment of 200 bottles of printer’s ink sent to France, not one was cracked.5
Panniers had to be dropped through the jump hole of a Halifax which was 40 in in diameter. To achieve a reasonable accuracy and despatch rate a weight limit of 120 lb (54.4 kg) was imposed for all packages. Under certain conditions this could be increased to 140 lb (63.5 kg) but a second despatcher had to be included in the crew.
Although in the case of containers a compromise parachute size of 22 ft had been agreed upon in late 1943, the parachutes used with the panniers varied with their weight. The recommended chute sizes for use with panniers of different weights are given in Appendix F.
Because of the very limited storage space available in the fuselage of a bomber, the Halifax could carry only six packages; the Stirling MkV ten packages; and the American B24 Liberator twelve packages.6
Improvements in the handling of panniers could be achieved by the use of a roller conveyor but, as detailed later, these were not fully operational in Europe before the war ended.
PACKING TRIALS AND DROP TESTING
Of primary importance was the need to ensure that loads dropped by parachute were not damaged on impact. Thus the development of methods of packing containers and panniers assumed a high priority. It is relevant to recall that in those days packaging techniques were in their infancy. None of the modern methods involving the use of bubble-packs, expanded polystyrene and vacuum forming was available and reliance had to be placed on various hessian and coconut fibre-based materials such as rubberised Koran and Hairlock. A highly desirable property of a packing material is that it should absorb energy when deformed. Highly elastic material such as Sorbo rubber, though at first sight ideal, had the disadvantage that it absorbed little energy so that rebound could cause as much damage as the original shock. An additional problem arose when, for logistical reasons, it was necessary for containers to carry a mixed load of explosives, ammunition, detonators and fuses. Great care had to be taken to ensure the compatibility of the contents by stipulating that sensitive items were not to be packed in close proximity. This led to the specification of a large number of ‘standard loads’, for each of which an appropriate packaging was devised and drop tested.
Early drop testing was carried out from a tethered barrage balloon at Cardington. As the pressure of work built up the facilities at Cardington became overloaded and the simpler method of dropping from a given height on a gantry onto a concrete slab was adopted. These tests were carried out at Henlow and Station IX. The choice of height was based on earlier experiments on the effects of dropping with different parachutes, supported by the theoretical considerations outlined in Appendix F. The effect of dropping a container weighing 330 lb (150 kg) on a 22 ft parachute was thus simulated by dropping from 12 feet, which gives an impact speed of 8.3 m per sec or 27 ft per sec. Panniers were dropped from 5 feet to take account of the lower speed of 17 ft per sec with which they impacted the ground.
In addition Country Sections had a wide variety of special needs which taxed the ingenuity of the packers. Particular problems arose when camouflaged items were involved. Thus W/T sets and S-phones, besides being included in standard packs, were often concealed in metal drums or similar common commercial boxes. Among other unusual loads which were packed and tested successfully were Mk I Folding Canoes, a printing machine, battery chargers and their steam generators, and medical kits.
But there were failures from time to time. Occasionally containers burst open and scattered their contents; this was attributed to failure of the locking devices arising either from a manufacturing fault or from the
neglect of the packer to ensure that the safety pins were correctly inserted. On other occasions pilots of stores-dropping aircraft expressed concern that some containers were catching fire or even exploding during their descent. No conclusive evidence for the cause of this was established. Containers would have carried explosives, incendiaries and ammunition but the detonating devices should have been packed separately and insulated from the shock accompanying the development of the canopy. It was known that it was possible for one particular fuse, the PR5, to be activated by strong vibration and these failures could probably have been caused by premature activation resulting from inadequate packing.
A general guide to parachute packaging was prepared in collaboration with Sqn Ldr Bunn at Henlow and circulated to Missions and Packing Stations but no copy has survived.
Lightweight Containers
The ASR Section was concerned with the development and testing of several other containers.
Early in 1943 at about the time that preparations for the Second Front accelerated, metal H- and C-type containers became scarce and attempts were made to develop an alternative lightweight container. A papier-maché version known as the ISRB Lightweight Container was designed and tested. Production prototypes were demonstrated to Country Sections in July 1943 and specifications and working drawings were prepared for it to be put into production if the shortage of metal containers continued. At the same time the Army issued a War Office specification for a lightweight container having a higher payload than currently available to Airborne Forces, but it had to be collapsible for ease of transport and storage. The ISRB container did not meet the latter condition. The RAE designed the Y-type container in a strong canvas material to meet this specification. A similar US Plastic Container (Navy Type A.10) was made of cloth impregnated with cellulose acetate. It weighed only 50 lb but was designed, apparently, for external carriage and needed modifications to fit British bomb racks.
In the event the supply of metal containers improved and work on lightweight containers ceased late in 1944.
Waterproof Containers
It was realised early that it would be a great advantage if containers were waterproofed so that heavy rain or landing in ditches or streams would not harm the contents. The requested operational requirements varied from being unaffected by severe weather conditions, such as in a monsoon, to remaining watertight after immersion in water. Containers were often used to store materials for long periods, so watertightness was an important requirement. In March 1943 attempts were made to provide tight sealing of both C-type cells and H-type containers. Experiments started at Station IX to find a suitable design of sealing ring, but this proved a difficult problem. In particular, any distortion of the metal caused by the landing or the impact with the water surface would destroy the sealing. In earlier models the rubber used for sealing did not stand up to tropical storage conditions and various components rusted easily, making the catches difficult to operate. By April 1944 prototypes had been tested with moderate success but further modifications were needed to ensure that the sealing rings remained correctly aligned after dropping. Even so, it could still not be guaranteed that H-cells remained fully watertight after dropping. Finalisation of design details and production was handed over to MAP early in 1945 and urgent action was being taken to get the modified containers available for the next moon period in March/April. But by now the main use was likely to be in the Far East. A partial solution was afforded by providing waterproof liners for the cells.
The K-Type Container
A much more rigorous Operational Requirement came originally from the Danish Section and led to the development of the K-type container. The basic concept was that watertight containers would be dropped at night into fishing areas at sea or in lakes. They would sink but would be recovered later by fishermen going about their normal business. The requirement was thus for a robust container which could be dropped into water, sink to the bottom and remain watertight. After a suitable delay it would release a buoy attached to a coloured float of the kind used locally. The container would have a ballast weight sufficient to overcome its buoyancy but which could be detached by pulling on the line attached to the buoy. The container would then float to the surface and be hauled aboard a fishing boat without attracting attention.
There were a number of technical problems to be overcome and ASR Section worked closely with RAE, MAP and the manufacturers on the detailed design. It was basically a cylinder of about the same dimensions as conventional containers, closed at one end while the other was fitted with a watertight lid which could be opened and closed easily. Attached to the base of the cylinder by a release catch was a solid block heavy enough to sink the container. The release catch could be activated by a sharp tug on the float line, releasing the ballast block and allowing the container to come to the surface. To avoid detection the parachute was to be weighted so that it remained submerged but was attached to the container so that it too could be recovered.
Among the problems to be solved was the design of a reliable closure for the lid which would not be distorted by the impact with the water, which implied in turn that the container had to be strongly constructed. The mechanical action of the release catch had to be robust and reliable. The delay switch releasing the float was developed from the very early water-activated switches which had been developed by MI(R) and Section D already in use for other purposes. The delay in releasing the float was to allay any suspicion that an aircraft flying over was dropping stores: delay times of between one and three days were requested. Preliminary testing of the individual components was carried out at Station IX and by the end of April 1944 six containers were ready for User Trials which were carried out in May and June.
The final dropping trial took place 2½ miles offshore from Troon in Ayrshire. For this a somewhat aged Wellington bomber was borrowed from Prestwick (arranged courtesy of AL Section). Everett acted as despatcher while other members of the Section observed from below. It was a stormy night and the first take-off was aborted when the cockpit canopy blew open. On the second attempt the four containers were dropped successfully at two-second intervals on a straight course down the Firth of Clyde. The parachutes were observed to open correctly.
The following morning a party went out on a borrowed launch to recover the containers. Three bright red floats were soon identified and a dinghy was launched to test the ease with which the containers could be manhandled over the stern of the boat. A ciné record of this was made but does not seem to have survived. The sea was moderate and no difficulty was experienced in the recovery. All three containers remained watertight. However, despite an extended search the fourth buoy was never found so its container, filled with explosives and incendiaries, lies somewhere on the sea bed. Although the loss was notified to the Admiralty, no attempt, as far as is known, was ever made to locate it.
Meanwhile, production was delayed in part by the fight to get priority for the supply of material for the special 14 ft parachute which was also needed for the RAF’s Fragmentation Bomb. By December fourteen containers were ready for operational use.
The first operational drop was over Denmark but was subject to delays due to bad weather and the fact that the proposed DZ was covered by thick ice, a circumstance not envisaged in the OR. It was eventually carried out on 28 February 1945. The reception committee was greatly impressed by the increased security imparted by the technique. The Germans were unfamiliar with this kind of supply drop and had they seen an aircraft would probably have thought it was laying mines in coastal waters. But to allay any suspicions the reception committee left retrieval of the containers for two days. When they did bring the stores to the surface they were in good order but they identified three problems: the container lid was difficult to remove, the container was difficult to unload and the buoys were too conspicuous. The original OR specified that the floats should be coloured to match those used by fishing boats in the area of the DZ. However, it was pointed out after the first drop
that the appearance of a large number of buoys overnight might raise suspicions and that it would be preferable to have some of them camouflaged, as ducks for example; but not so well camouflaged as to make them difficult to see. Moreover, a delay of 48– 72 hours before they were released to the surface would give a longer time for any suspicions to die down. As the war was coming to an end, the last drop – with a scatter of only 150 m – was made on 23 April near Lendrup harbour between the Logstor area and Livo Island in northern Denmark. Retrieval was delayed for 5 days, but the contents had remained dry.7
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