The Battle of Britain (18 page)

Accordingly, two British engines, one of them the Merlin, were tested and developed to run on 100-octane, which was available only from abroad. Eventually an outstanding fuel called BAM.100 (British Air Ministry 100) was developed and the first cargo was shipped to Britain from the the Esso refinery at Aruba in June 1939. The Air Ministry stockpiled the valuable fuel, which was dyed a distinctive green: this fact remained unknown to German intelligence. This stockpiling went on throughout the war, but in May 1940, when the chips were down and everything counted, the RAF began to use the special fuel, in Merlins of Fighter Command. At a stroke the maximum boost was doubled, from 6lb (1.36ata) to 12lb (1.82ata), increasing maximum power from 1,030hp to 1,310hp. This significant increase made a major difference to the Hurricane and Spitfire. It brought the former pretty much up to the level of the Bf 109E, when it would otherwise have had a distinctly lower performance. As for the Spitfire, it gave that aircraft a vital edge, despite the fact that its rival was smaller yet had a bigger engine. This again was long-distance foresight.

A further factor was that, whereas both the Hurricane and Spitfire had gone into service with crude fixed-pitch two-blade wooden propellers, by mid-1940 almost all had three-blade constant-speed
propellers giving better take-off, faster climb and better high-speed performance. One of the first re-propellered Hurricanes was used by F/O ‘Cobber' Kain in France to shoot down a Do 17 from 27,000ft (8,230m), and it was officially stated that the enemy bomber could never have been intercepted without the improved propeller. Fitting controllable-pitch propellers, followed by constant-speed propellers, was a crash programme involving round-the-clock work by the two manufacturers, de Havilland and Rotol.

It is difficult to explain the apparent lack of interest shown by the Air Ministry between the World Wars in aircraft armament. To some degree it may be explained by lack of money, but at the eleventh hour available foreign guns were evaluated and the choice fell on the rifle-calibre Browning and 20mm Hispano-Suiza. Both dated from World War I, but in the absence of anything newer preparations were urgently made to have both guns manufactured under licence in Britain. Because of their ancient design, neither gun was really competitive in the context of World War II, but they were at least eventually made reliable. The Hispano cannon was made by British MARC (Manufacturing and Research Co.) at Grantham, but it played only a very minor role in the Battle of Britain (though Hawker Aircraft had proposed a four-20mm Hurricane in January 1936). Most of the cannon-armed aircraft in the Battle were Spitfires, but very few pilots at that time thought the bigger gun an advantage. The Browning modified to fire British rimmed 0.303in ammunition was virtually the standard gun of the RAF fighters and it was made under Colt Automatic Weapon Corporation licence by BSA (Birmingham Small Arms)

Of course, both the new monoplane fighters had their guns mounted well outboard inside the wings, where almost all previous RAF fighters had had them in the fuselage. In the traditional installation the pilot could clear stoppages (he often carried a mallet for this purpose) and recock the weapon to continue firing. He could no longer do this with the Hurricane and Spitfire, and moreover the Dunlop company had to devise and supply electrically controlled pneumatic cocking and firing systems. Other companies provided hot air ducts to prevent the gun lubricant from freezing at the unprecedented heights at which combats could now take place.

Of course, guns are useless unless they can be aimed accurately. Unless a fighter is directly astern of its target the pilot has to ‘aim off'. He has to
aim at a point ahead of the enemy so that the bullets and the enemy aircraft (EA) arrive at the same place at the same time. In extreme cases the lead angle – the angular distance between the sightline to the target and the direction of aim – can be as great as 11 degrees. Few pilots survived long enough in combat to master this, so from the mid-1950s the Royal Aircraft Establishment at Farnborough tried to devise a sight that would do this automatically. In 1937 it finalised the design of the gyro gunsight (GGS), in which a rapidly spinning mirror is mounted on a Hooke's (universal) joint connecting it to a hemisphere of thin copper rotating between the poles of powerful magnets. This sight, for the first time, enabled the pilot to fly his fighter so that an illuminated ring was centred on the target, the lead angle, and even the gravity drop of the bullets, being automatically allowed for.

Many prototypes of the GGS were used to great effect in the Battle of Britain, but they were still the exception. The sight was licensed to Ferranti, whose new factory at Edinburgh was built to make the GGS and began deliveries in 1942. The standard sight in 1940 was the newly introduced reflector sight, which projected an illuminated ring, usually with a central cross, on to an oval glass behind the armoured windscreen. The only adjustment the pilot could make was to vary the size of the ring, and if he knew the span of the target he could obtain a range indication (most pilots in the Battle tended to open fire at far too long a range). The Hurricanes and Spitfires almost always had a traditional ring-and-bead sight as well. Some pilots in 1940 actually used this, as being simple and fool-proof, but it was really provided as a standby aiming system in case of failure of the electrical system.

Unquestionably, the greatest aid to accurate aiming was looking at the results of practice combats on cine film. The need to carry a ‘camera gun' was agreed only immediately before the war, and it proved its worth from the first day. Apart from being a marvellous training aid it was a reliable witness to actual combat, and could confirm or refute a pilot's claims made in his Combat Report. All the cameras used by Fighter Command in the battle were standard 16mm products from Williamson Manufacturing Co., of London (Willesden) and Reading.

In the Battle of Britain radio assumed a totally new importance. During the 1930s it had been standard practice for defending fighters to mount a standing patrol across the expected line of approach of enemy bombers and at what was considered a likely altitude. In actual war this would have been
far too costly in terms of engine hours, fuel, pilot fatigue and on many other counts, and with the Luftwaffe able to attack from an arc ranging from Norway to Spain the whole idea would have been impractical. Radio had been introduced by the British to enable ground controllers to transmit details of enemy attacks to squadrons on standing patrol, the source of the intelligence being the Observer Corps. Radio also enabled squadron and flight commanders to issue commands to their pilots and of course in actual combat it was needed almost constantly by everyone involved, both to shout warnings and instructions and to listen for others.

The ubiquitous TR.9D was a high frequency (HF) set. It was connected to a wire antenna (aerial) loosely slung between a rigid mast projecting vertically above the rear fuselage and the top of the rudder. Despite careful screening of the engine ignition system, interference (static) was invariably obtrusive and often deafening. Probably more than half ‘The Few' were seldom able to understand the clipped bursts of noise that assailed their ears, and ‘say again' became one of the most common transmissions.

In 1939 Hawker's civil trial installation Hurricane G-AFKX was fitted with, among other things, the first very high frequency (VHF) radio, TR.1133. This worked with marvellous clarity, and it also needed only simple ‘whip antenna' offering hardly any drag, but it was fitted to only a few aircraft in the Battle of Britain. The first aircraft in service with VHF was Spitfire R6833 of No. 19 Sqn on August 20, 1940. It was to be 1942 before all the old HF sets had been replaced in Fighter Command.

Two completely new radio functions were introduced just in time for the Battle. One was IFF (identification friend or foe), a semi-automatic method in which a friendly radio station, especially in a fighter, would ‘interrogate' all aircraft in the vicinity. Friendly aircraft would instantly and automatically respond with a very short coded signal, which would be changed frequently to prevent it from being copied by the enemy. Absence of such a response would brand the aircraft as ‘not friendly', and in wartime this tended to be equated with ‘hostile'. The other new asset was radio D/F. Direction finding by radio was not new, but it had never before been available to enable a ground controller to keep track of the position of fighter formations. Each Sector Commander had two or three specially built D/F stations which received signals automatically transmitted at regular intervals by particular fighters, giving an almost immediate indication of bearing.

In 1934 the Air Ministry, in the person of scientist Percival Rowe, became concerned that the file on how science could help air defence contained only a few more or less useless pieces of paper. A special committee was formed, and in January 1935 the Director of Scientific Research, Dr H. E. Wimperis, sought the opinion of the top radio expert, Dr Robert Watson Watt, on whether it would be theoretically possible to build a ‘death ray', an idea much in vogue in the popular press and works of fiction. The eminent physicist replied that, for practical purposes, the answer was ‘No'. Almost all civil servants would have left it at that, but ‘Wattie' added a little comment that had not been asked for, and by so doing he changed history and almost certainly changed the outcome of the Battle of Britain and of World War II.

He casually pointed out that, to destroy an enemy bomber with a ‘death ray' you had to aim the ray precisely at the bomber. No way of doing this existed but Watson Watt suggested that, though this had not been mentioned, it should be possible to use radio methods to detect and locate hostile aircraft. The committee studied the idea on January 28, 1935. On February 26, Rowe and two assistants parked an ancient van in a field about ten miles from the powerful BBC transmitting station at Daventry. They set up a receiving antenna and connected it to a cathode-ray tube (CRT). Soon they heard the drone of Kestrel engines. It was a biplane Heyford bomber, flying a prearranged track overhead. As expected, the bright green line across the face of the CRT grew a small spike or ‘blip'. As the bomber passed overhead the blip moved along the display and grew until it was big and impressive. Then it shrank, as it moved to the other side of the tube. Rowe could not only follow the bomber's track but he could have told the pilot that he was a few hundred feet off to one side of the prescribed route.

This triggered off a gigantic programme of thinking, planning, designing, building, manning and testing the first air-defence radar chain in the world. It started on July 24, 1935 when an historic set of photographs was taken of the CRT display at the pioneer RAF radar station at Orfordness in Suffolk. Clearly visible, in eight pictures of the display from 1126hrs to nearly 1216hrs, were the blips (echoes) from a Westland Wallace, two Hawker Harts, a single Hart and an unknown aircraft. By the outbreak of war the Chain Home (CH) stations sprouted their huge 350ft (107m) steel towers all round the coast from the Isle of Wight to the tip of Scotland.

The CH stations could clearly see aircraft at a height of 15,000ft (4,572m) for a distance of at least 40 miles (64km). In some cases the range was greater, and during the Battle of Britain the vital stations from Ventnor (Isle of Wight) round to Kent could actually watch the Luftwaffe formations forming up over France and Belgium before starting to cross the Channel. These big stations operated on a wavelength of 33ft (10m) They could not detect aircraft flying at low levels, and so from September 1939 a second row of stations was added to plug the gap. Called Chain Home Low (CHL), they operated on only 5ft (1.5m) wavelength with rotating antenna arrays on top of 185ft (56m) and 20ft (6m) towers. They could see a fighter speeding in at only just above sea level, out to a distance of up to 30 miles. By August 1940 the CHL stations stretched right round South and East England and up to the Shetlands.

Thus, throughout the Battle of Britain, every raid by the Luftwaffe was detected as soon as it took off and kept under continuous radar surveillance as it approached the English coast. In the crucial years 1937–39 the entire RAF defence network was perfected, the information from all the radar stations being collected and sifted at Filter Centres and the overall battle control from Sector, Group and finally Fighter Command plotting rooms, the command room being at Bentley Priory, Stanmore. The central feature of the Operations Room at Fighter Command was a giant map of Great Britain, arranged horizontally at table height. The land area was divided into about 130 Warning Districts, in each of which, depending on the threat situation, a Warning or an All Clear would be sounded, the first by a distinctive rising and falling note on powerful sirens and the latter by a steady note. There were many subsidiary arrangements, all concerned with the population at large and quite separate from the direct telephone lines to the Fighter Command stations.

The radar observers who, like the plotters, were mainly members of the Womens' Auxiliary Air Force (WAAF) soon became extremely skilled not only at estimating target ranges, which were relatively easy, but also target bearings, heights and numbers, which were more difficult. The existence of this nationwide radar barrier meant that if an RAF squadron scrambled it was almost bound to meet the enemy and engage in combat. Detailed instructions on the enemy's movements could be radioed by the Controllers right up to joining battle, with the hoped-for added advantage of getting into a favourable (eg, up-sun) position beforehand.

In 1940 the CH and CHL radars looked out to sea but had very limited performance in the other direction, over land. Therefore, enormous responsibility continued to be placed on the Observer Corps, which expanded in numbers to 32,000, refined its methods and manned 1,400 posts during the Battle of Britain. The Corps received the prefix ‘Royal' in 1941. Among their many duties was immediate and accurate reporting of the location of every crashed aircraft and every parachuted pilot or crew-member, both over land and off the coast. In the latter case the RAF's ever-alert air/sea rescue service would swing into action, using fast power boats and Supermarine Walrus amphibians to fish friend and foe alike out of the Channel.