SOE

by Fredric Boyce

  The ongoing developments previously under AL were transferred to ASR. Work on these and other developments are discussed in the following sections.

  Information on the use of air supply by SOE was recorded in a series of files under the general heading ‘Planning and Supply of Air Dropping Equipment’. Unfortunately, most of these are missing. There is no trace of the fifty or so files with the archive reference numbers 250/2.1 to 250/2.54. However, the Bimonthly Progress Reports of the ASR Section from April 1944 to May 1945 have been traced, together with the ‘History of the Air Supply Research Section’, written by Everett in August 1945.

  To aid in operational planning the ASR Section compiled the ‘ISRB Air Supply Handbook’ which included tables of wind drift, drop height and wind speed as well as data on parachutes and size of bomb racks in various aircraft. Although produced in limited numbers this was said to have been found of great assistance, not only to SOE but also to the Army Airborne Transport Development Centre. Copies of this handbook were reputed to have been sent to the War Office but none has been found.

  General Technical Considerations

  The basic requirements of air supply were that stores had to arrive in enemy-occupied territory undamaged and delivered into the right hands at the right time. Since supply operations usually took place at night and the stores included fragile items such as radio sets and the accumulators to power them, the problems were considerable.

  The successful outcome of an airdrop depended first on the location and identification of the dropping zone (DZ) and then on the accurate dropping of the stores. Once the DZ had been located the pilot had to fly in at a predetermined height and speed and on a course taking account of wind speed and direction, and the containers had to be released at the appropriate moment over the DZ. Since most operations were carried out in moonlight, the skills demanded of the aircrew were considerable: it was far too easy to run in too low so that the parachutes did not fully develop before the load struck the ground, or to be overcautious and drop from too great a height, leading to excessive drift in the wind. The requirements were much more stringent if agents were to be dropped at the same time. The design of equipment for such operations involved making a compromise between the parachute size, the weight of the full container and the amount and nature of the packing material. The objective had to be that the container spent as little time as possible in the air, commensurate with an impact velocity which did not damage the contents. The impact speed and hence the amount of packing material required could be reduced by increasing the size of the parachute. But this meant that the loads remained for a longer time in the air, so increasing the wind drift. For a run-in at a height of 500 ft the load was in the air for less than half a minute. Even with a wind speed of 10 mph this meant a drift of 150 yd from the point of release. With container despatches at intervals of half a second, the length of a stick of ten containers dropped from an aircraft flying at 130 mph would be some 300 yd. Moreover, if a number of containers and packages of different weights were despatched on the same run, then to minimise scatter on the ground the parachutes had to be chosen such that the rates of descent of the different loads were roughly equal.

  The above considerations determined the choice of the appropriate combination of parachute size, weight of load and packaging requirement for a given operation; in the early days these were reached by trial and error. An explanation of the optimisation of parachute sizes is given in Appendix F.

  Choice of Dropping Zones (DZ) and Reception Committee (RC) Procedures

  In the early days before organised Resistance groups had been established, agents with W/T sets were dropped ‘blind’ into areas where there was reason to believe that they could make contact with previously identified friendly nationals who would work with them to set up a local organisation. But time and time again, as records confirm, such drops were made far away from the intended location – sometimes as much as 50 km (32 miles) distant. And often the agents were quickly arrested. It was not until agents with W/T operators were able to make contact with London that Reception Committees at a precisely defined DZ could be arranged.

  In choosing a DZ certain minimum requirements had to be satisfied. It was recommended that to allow for variable wind drift, the DZ should be at least 600– 800 yards square and preferably in level country. It had to be free from trees and other obstacles for some 200 yards outside its perimeter. It was particularly important that the aircrew were well briefed as to useful landmarks to enable them to come within a few kilometres of the DZ. The choice of dropping point would be influenced not only by the technical requirements but also by operational factors such as the location of enemy units, the availability of members of the reception committee, and of means of transport to accessible concealment or storage sites.

  Signalling Devices

  Supply operations were normally limited to a period of a week or so on either side of the full moon. The aircrew had therefore to navigate (as in a bombing raid) by dead reckoning backed up by identification of landmarks such as rivers and railways. When the reception committee heard the sound of an approaching aircraft visual contact by means of lights or fires had to be established, and a prearranged procedure followed for the mutual recognition and clear identification of the DZ and aircraft. The detailed methods depended on local circumstances. In remote areas such as the Balkans, where the enemy presence was thinly spread, it was possible to use fires to attract the attention of the aircraft. They were not appropriate in closer country where, even if not observed by the enemy at the time, they left tell-tale evidence of a supply drop. An alternative sometimes recommended where fuel for a fire was not available was to fill a large tin, such as a petrol can cut in half, with soil or sand, wet it thoroughly with petrol or paraffin and set it alight. This had the advantage that it could be extinguished quickly and carried away in the case of emergency. In some cases, especially in the Far East later in the war, signal flares were used. However, in most of Europe more clandestine methods had to be employed.

  Light signals to aircraft had to be capable of being seen by aircrew on the lookout but not so obvious that they would attract unwelcome attention on the ground. The more sophisticated signalling lamps such as the Aldis and the Admiralty Automatic Morse Signalling Lamp were not readily available and were in any case somewhat bulky and not easily concealed. Moreover, they were too bright for clandestine use. Reliance had therefore to be placed on simple domestic torches or bicycle lamps which might be available locally or could be dropped from the air. The standard issue SOE torches were modified Ever Ready 2-cell torches of somewhat flimsy construction. The dry cells available at that time were of the now obsolete zinc/carbon variety of relatively low capacity. They were optimistically said to have a lifetime in continuous use of between three and five hours, and a relatively short shelf life. The switches on the torches tended to corrode and were not waterproof. It was soon realised that these torches were not really robust enough for satisfactory use in the field. Several attempts were made to design a waterproof torch which could withstand immersion in two feet of water (e.g. in a ditch). Only moderate success was achieved and difficulty was found in waterproofing the switch – something that would present no problems with today’s materials. None was put into production and later a US torch with improved but not perfect properties was adopted. Although the SOE catalogue describes a ‘French Torch’ as an exact replica of a French make, these were never submitted to a user trial so their performance is not known.

  The SOE torches were supplied with a set of coloured filters: red, amber, green and blue to assist in the identification of DZs. Over a period of a few months several trial/training operations were carried out to test the various methods of locating and identifying DZs. In a trial on 5 August 1943, a clear night four days after the full moon, an aircraft flying at 1000 feet was able to pick out visual signals at a range of five miles. Green and red filters were most easily seen while orange and amber were less easily d
istinguished. These and other trials in conjunction with the Training Sections also compared alternative layouts of reception torches at the DZ.

  As time passed more sophisticated methods were being evolved. The Eureka/Rebecca system developed by the Telecommunications Research Establishment (TRE) involved a transmitter (Rebecca) in the aircraft which was tuned to respond to Eureka on the ground at the DZ. This enabled the aircraft to be guided to within a reasonable distance of the DZ when visual contact using torches could be made. There is evidence that this system, although used successfully by Airborne Forces, was less popular with SOE. Among other things, Eureka was heavy, weighing nearly 1 cwt (51 kg), and was difficult to conceal and transport, although the Camouflage Section devised several ways of disguising it.

  Meanwhile, as described in Chapter 12, the Radio Communications Division at Station IX had taken up the idea dating from 1940 of developing a short wave radio telephone – the S-phone. This enabled the aircraft not only to home in on the ground station (carried on a pack by the operator), but also to pass verbal messages between them. Despite early technical problems, the S-phone proved to be of immense value in raising the efficiency of air-dropping operations. Whereas in the early days a major cause of failure of an operation was the inability of the aircraft to locate the DZ, this was greatly reduced when homing devices were used. Further developments of the Eureka/Rebecca system and trials of alternative radio beacons and similar American systems were being planned when the war ended. The use of infra-red devices for air/ground signalling were also under active discussion, although nothing more than a few preliminary experiments had been done at Station IX.

  As the opportunities for daylight operations increased (especially by the US Air Force), consideration was given to alternative methods of organising daylight receptions. It was found that the American fluorescent ground markers were considerably more effective than the British versions. An alternative method of attracting the attention of aircraft (originally for Air/Sea Rescue use) was the employment of mirror devices, the reference beam of which could be aimed accurately. Two very efficient models were tested. Standard Army smoke generators were found to be useful in indicating wind direction in daylight drops.

  PARACHUTES

  The development and testing of personal parachutes was in the hands of MAP, SOE having no direct involvement. The standard British parachute (at first the type A, later the type X) was made of silk, 28 ft in diameter, and was designed to give a rate of descent for an average person of around 17 ft per second. SOE as users had good reason to be especially concerned with their reliability. Work was proceeding in the spring of 1943 on improving the reliability of the parachutes, some of which had failed to develop properly. The experimental A-type rig had been abandoned and investigations into the tangling and twisting accidents with the X-type packs had reduced the failure rate which in training had been about one in five thousand drops. Nevertheless, failure of the personal parachute to open was a rare occurrence and often the reason could be identified with causes unrelated to the parachute itself. No overall figures are available for European operations but the French Sections had a total of six fatal parachute casualties – none of which was during training. One in July 1942 resulted from a bad landing at night on rough ground, at least one in January 1944 from being dropped from too low a height, and one from failure to hook up the static line properly. There were only two cases in which it was suspected that the cause was a faulty parachute but a reliable record of the overall failure rate, attributable to equipment failure, has not been found. Several serious but non-fatal accidents were attributed to dropping from too low a height, caused by either poor weather or pilot error.

  Supply Dropping Parachutes

  Official tests of supply dropping parachutes for MAP were the responsibility of the RAE who arranged for them to be carried out by Sqn Ldr Bunn at Henlow and by AFEE. The parachutes used by SOE for supply dropping were standard cotton C-type of diameter 28 ft and later 22 ft. In general SOE was not directly involved although close liaison was maintained with Sqn Ldr Bunn. In dropping tests which took place at Henlow in June 1943 a comparison was made between cotton and Celanese canopies and the RAE cotton type showed marked superiority.

  Drops were usually made from a height of only a few hundred feet to improve the accuracy of targeting the drop zone. This left little time for a parachute to develop and if it encountered adverse conditions in the aircraft’s slipstream, a hesitation of only a couple of seconds might mean the difference between the successful delivery of much needed stores and the salvaging of severely damaged goods from a wrecked container. Attention turned to the reliability of parachutes after storage, it being known that a canopy stored in a damp atmosphere, perhaps with the weight of others on top of it, was likely to develop more slowly than a dry, freshly packed one. Thus it was preferable for parachutes to be hung in sheds until required for use. The problem was more acute in tropical climates and considerable effort was made to design a waterproof package for parachutes.

  There are no reliable statistics on the parachute failures in supply dropping in Europe, although ASR Section prepared an analysis of failures reported from the field in the last six months of 1944. More detailed records were kept for North African operations, but these do not appear to have been preserved. However, it was claimed by one agent operating out of Massingham, North Africa, that in one area one fifth of the supplies were lost either because the parachute failed or the container burst open in mid-air or on impact. Other isolated examples in which containers burst on impact and the contents caught fire were reported from time to time by British agents. Similarly, the supply dropping in support of the 14th Army in Burma in April 1945 was plagued by parachute failures. On one major operation, among 131 drops there were 50 parachute failures. In many cases, as recounted in Chapter 16, the cause could be traced to failure of those responsible for loading containers onto the aircraft, or to damaged or badly packed parachutes. Rigorous checks on a subsequent operation reduced the failure rate to zero.

  Parachutes for High Speed Dropping

  The standard speed for dropping loads of up to 300 lb (136 kg) was 130 mph. To enable higher speeds to be used RAE designed a parachute which tests at AFEE showed could be dropped at 250 mph with a load of 350 lb (158 kg), while a load of 500 lb (227 kg) could be dropped at 200 mph. This new parachute, designated Type R, was of shaped gore design with a flying diameter of about 20 ft. (The gore is the section of canopy fabric between rigging lines running from the peripheral hem to the crown.) The rate of descent was practically the same as that of a 28 ft flat chute with a comparable load. This promised SOE the possibility of raising the weight of the standard container to 500 lb (227 kg), subject to packing and dropping trials. Production of this parachute commenced in February 1945 with the expectation of 10,000 being available in two months. However, ASR Section plans to test the new parachute with SOE operational loads were suspended pending the decision whether to deploy this parachute in Europe and in the Far East.

  The American G1 Parachute

  Problems arose when supplies of British parachutes became critical and American G1 cargo dropping parachutes became available. These differed from British parachutes in that while the British chutes were made of cotton, the US types were of a rather closely woven viscose. The ASR Section was called upon to check these parachutes with SOE containers under SOE dropping conditions. The first tests were carried out at Henlow in May 1944 when four fully loaded containers were dropped from a Whitley aircraft flying at 135 mph. The result was alarming. Two parachutes failed and one container filled with incendiaries caught fire on impact and burned furiously. The firework display was brought under control by the Station Fire Brigade. This was the first trial to be recorded on cine film and demonstrated the value of having a proper record of trials. On examination of the chute it was found that the rigging lines and lift webs were badly torn. The consequent doubts about the suitability of the G1 chute for SOE operations we
re strenuously opposed by the Americans and led to some strongly worded exchanges. Further trials were carried out in June by both ASR Section and AFDC. In the ASR trials, out of a total of nine drops at 150 mph and with loads of 300 lb (136 kg) two parachutes failed completely while three parachutes were damaged leading to substantial damage to the containers. A failure rate of five out of nine was regarded as unacceptable. Meanwhile, AFDC dropped 48 panniers of 330 lb (150 kg) at the lower speed of 120 mph and had only one failure. The interim conclusion was that these parachutes should be dropped at a maximum speed of 140 mph and loading of 300 lb (136 kg). This was endorsed in September by MAP who, however, reduced the maximum speed to 135 mph. The British results were not accepted by the Americans who proceeded to arrange joint trials with ASR Section. In these the drops were from B24 Liberator bombers and were covered by air-to-air cine film. To ASR Section’s consternation the Americans were so confident of their ability to drop accurately that they proposed to drop into the courtyard of historic Howbury House east of Bedford which they had requisitioned; but under pressure from the ASR Section they were persuaded to drop into the adjacent fields. The written report of these trials has not been found and the conditions were not recorded. However, the cine film which has survived confirms that of some dozen drops only one parachute appears to have ‘candled’. It was found that for use with British containers some modifications were necessary to enable the chutes to be used with the British static line. ASR Section issued detailed instructions for these modifications and its assembly in November and this was eventually cleared by the Air Ministry in February 1945. Then a few weeks later, for reasons unknown, the Air Ministry ruled that this parachute should not be used with British containers. The sheer number of parachutes required was astonishing. Operations envisaged required a total of 212,000 parachutes between January and April 1944 alone, and up to the end of June a staggering 1,220,000 parachutes were called for. This number would certainly have included those for the three-man Jedburgh teams dropped just after D-Day and for the supply drops to the Maquis after the invasion. Whether they also catered for the Airborne Forces involved in the D-Day drops into France is not clear. This quantity could not be met by ordinary means, even with the help of a parachute factory set up in Cairo to make use of locally produced cotton and of the American manufacturing facilities. To relieve the situation, at least as far as the Far Eastern operations were concerned, hundreds of sewing machines, benches and treadle units were shipped out to India for local labour to manufacture parachutes in hastily created workshops.