The Hardest Day

The Hardest DayBungay 2000, p. 231. was a Second World War air battle fought on 18 August 1940 during the Battle of Britain between the German Luftwaffe and British Royal Air Force (RAF). On that day, the Luftwaffe made an all-out effort to destroy RAF Fighter Command. The air battles that took place on that day were amongst the largest aerial engagements in history to that time. Both sides suffered heavy losses. In the air, the British shot down twice as many Luftwaffe aircraft as they lost. However, many RAF aircraft were destroyed on the ground, equalising the total losses of both sides. Further large and costly aerial battles took place after 18 August, but both sides lost more aircraft combined on this day than at any other point during the campaign, including 15 September, the Battle of Britain Day, generally considered the climax of the fighting. For this reason, Sunday 18 August 1940 became known as "the Hardest Day" in Britain.

By June 1940, the Allies had been defeated in Western Europe and Scandinavia. After Britain rejected peace overtures, Adolf Hitler issued Directive No. 16, ordering the invasion of the United Kingdom. The invasion of the United Kingdom was codenamed Operation Sea Lion (''Unternehmen Seelöwe''). However, before this could be carried out, air supremacy or air superiority was required to prevent the RAF from attacking the invasion fleet or providing protection for any attempt by the Royal Navy's Home Fleet to intercept a landing by sea. Hitler ordered the Luftwaffe's commander-in-chief, ''Reichsmarschall'' Hermann Göring, and the ''Oberkommando der Luftwaffe'' (High Command of the Air Force) to prepare for this task.

The primary target was RAF Fighter Command. In July 1940, the Luftwaffe began military operations to destroy the RAF. Throughout July and early August, the Germans targeted convoys in the English Channel and occasionally RAF airfields. On 13 August, a major German effort, known as ''Adlertag'' (Eagle Day), was made against RAF airfields, but failed. The failure did not deter the Germans from persisting with air raids against the RAF or its infrastructure. Five days later came the Hardest Day.

Background

The Luftwaffe was detailed to destroy Fighter Command before the planned invasion of Britain could take place. The ''OKL'' hoped that the destruction of the British fighter defence would force the British to come to terms by air power alone and the very risky Operation Sea Lion would not be needed. The enormous numerical superiority of British naval forces over their German opponents made a crossing of the Channel very dangerous, even with air superiority. Furthermore, the aircraft losses of the spring campaign had weakened the Luftwaffe before the Battle of Britain, and it could not begin its campaign against Fighter Command immediately. It was forced to wait until it had reached acceptable levels before a main assault against the RAF could be made in August 1940.

Until the Luftwaffe was ready to begin operations over the mainland, the first phase of the German air offensive targeted British shipping in the Channel. The raids rarely involved attacks against RAF airfields inland, but enticed RAF units to engage in battle by attacking British Channel convoys. These operations lasted from 10 July to 8 August 1940. The attacks against shipping were not very successful, and only 24,500 GRT was sunk. Mine laying from aircraft had proved more profitable, sinking 38,000 tons. The impact on Fighter Command was minimal. It had lost 74 fighter pilots killed or missing and 48 wounded in July, but British strength rose to 1,429 by 3 August, leaving it short of just 124 pilots. Still, the attacks succeeded in forcing the British to abandon the Channel convoy route and to redirect shipping to ports in north-eastern Britain. With this achieved the Luftwaffe began the second phase of its air offensive, attacking RAF airfields and support structures in Britain.

The month of August witnessed an escalation in air combat, as the Germans made a concentrated effort against Fighter Command.Holland 2007, p. 478. The first major raid inland and against RAF airfields came on 12 August, and the Luftwaffe quickly escalated its offensive. The Germans did not achieve a degree of success commensurate with their exertions on this date. Nevertheless, in the belief they were having considerable effect on Fighter Command, they prepared to launch their all-out assault on the RAF the following day. By 13 August, German air strength had reached acceptable levels. After bringing its serviceable rates up, the Luftwaffe carried out heavy attacks under the codename ''Adlertag'' (or Eagle Day), with 71 per cent of its bomber force, 85 per cent of its Messerschmitt Bf 109 fighter units, and 83 per cent of its Messerschmitt Bf 110 heavy fighter/fighter-bomber units operational. The day went badly for the Germans, who failed to impair Fighter Command and its bases or command and control system. This was due in large part to poor intelligence, which failed to identify Fighter Command airfields and distinguish them from those of Bomber and Coastal Commands. Still, the Germans pursued their strategy against Fighter Command on 15 August, suffering 76 losses. Undeterred, they prepared to make another large-scale attack on RAF bases on 18 August.

Luftwaffe plan

German intelligence suggested that the RAF was down to just 300 serviceable fighters on 17 August 1940, taking into consideration German pilots' claims and estimates of British production capabilities. In fact, there were 855 machines serviceable, with another 289 at storage units and 84 at training units. These resources were included in a total of 1,438 fighters, twice as many as at the beginning of July 1940. Expecting weakening opposition, the Luftwaffe prepared for a major action against RAF Sector Stations on 18 August.

The Luftwaffes plan of attack was simple. German bombers were to strike at the RAF airfields in the south-east corner of England. The most important airfields in this region, under the command of AOC (Air Officer Commanding) Keith Park and his No. 11 Group RAF, were the Sector Stations at RAF Kenley, Biggin Hill, Hornchurch, North Weald, Northolt, Tangmere and Debden. The first five were on the periphery of Greater London. Tangmere was in the south near the coast at Chichester, while Debden was north of London near Saffron Walden. Each of these airfields housed two to three squadrons and had its own sector operations room. From there, its fighters were directed from its satellite airfields into combat. There were six satellite airfields at Westhampnett, Croydon, Gravesend, Manston, Rochford and RAF Martlesham Heath; Manston and Martlesham Heath each housed two squadrons, the remainder each housed one. Finally, there was RAF Hawkinge, just inland from Folkestone. Not all of these airfields were targeted on 18 August.

Despite the failure of ''Adlertag'' and considerable loss rates on 15, 16 and 17 August, Kesselring convinced Göring that the only sound strategy was to continue to send heavily escorted bombers to destroy British airfields. Kesselring also advocated the use of ''Jagdgeschwader'' (fighter wings) in free-chase tactics. Messerschmitt Bf 109 single-engine fighters were to be sent out in advance of the main raids to force the British fighters into large-scale air battles which, in theory, would destroy RAF aircraft in combat and deplete the British defences. However, this time, Kesselring changed his operational methods. In consultation with Hugo Sperrle, commanding ''Luftflotte 3'' (Air Fleet 3), he chose not to scatter his effort against a large number of targets. Instead, he narrowed down the targets to a short list in order to concentrate his strength and striking power. Sector stations RAF Kenley, North Weald, Hornchurch and Biggin Hill were chosen as the prime targets.

RAF defences

Initial strategy and tactics

Up to the late spring of 1940, Fighter Command had been preparing to meet a possible air attack on the British Isles coming only from due east, from Germany itself; prior to the German victory in Western Europe. The possibility that France might fall and Britain would continue to fight on had not been considered. An air attack from Germany meant the Luftwaffe's bombers would operate beyond the range of their fighters and be vulnerable to attack. If twin-engine fighters, such as the Messerschmitt Bf 110s were used, they would be fighting at the limits of their range.Price 2010, p. 43.

It was also doubted that fast fighter aircraft could engage in dogfights. The g-force effect on the human body also seemed to suggest the prospect of air-to-air combat between fighters was impractical anyway. The threat they saw related only to the return-fire of the bomber's gunners. Before the war the effectiveness of return, or cross-fire, from bombers had been exaggerated by the Air Staff and Air Ministry.

This short-sighted belief had a detrimental impact on the tactical effectiveness of RAF Fighter Command until the summer, 1940. With German bombers perceived as the only prey, AOC Fighter Command Hugh Dowding and his planners devised a system and tactics which used unwieldy and tight fighter formations to bring the RAF fighters into combat with bombers, followed by set-piece tactics for the engagement. Because the bomber's return fire was considered so dangerous, fighter pilots were trained to open fire at long range, 300 to 400 yards, then break away without closing to short-range. These tactics, practised so thoroughly over the years, proved totally useless in the battle situation facing them over Britain in 1940.Price 2010, p. 44.

The tactics were also unsuitable for fighter-versus-fighter combat. Packed in tight formation, the RAF pilots were more concerned with keeping their position and not colliding with each other than they were keeping watch for the enemy. It made them vulnerable to surprise attacks by Bf 109s and Bf 110s. Even if the British fighters reached the bombers without interception, the chaos of modern aerial combat made it impossible to concentrate attacks with large, rigid formations. Pilots were also forced into paying far too much respect to the bomber's defensive capabilities. Attacks were broken off far too early and caused little damage to bombers. These tactical failures were evident during the battles in Belgium and France. Moreover, rushed training with pilots who were barely able to use the old tactical methods meant that airmen could not cope with much needed radical changes.

The V or Vic formation was developed in June, which made a greater emphasis on each pilot looking for the enemy, search capability and avoiding being taken by surprise. Still, it was inferior to German fighter tactics.Price 2010, p. 45.

German fighter tactics were more flexible. In the Spanish Civil War, Werner Mölders developed a new system of fighter tactics. The primary deployment was to use large numbers of Bf 109s on free-hunting missions, or sweeps, over the battle area. Instead of flying the standard V formation, used by many air forces, the Germans paired their fighters into ''Rotte''. It consisted of two fighters; a pilot and his wingman 200 yards abreast. Flying this way meant each could cover the others blind spots. If an enemy made an attack, the other could move in behind it to protect the other ''Rotte'' member. The ''Rotte'' could be expanded into a ''Schwarm'' (Swarm or Flight). The formation was eventually given the name "Finger-four". It offered maximum protection and all members of a ''Schwarm'' were on the lookout for threats and targets.

C3: Command, communication and control

At the operational level the British fighter defences proved to be far more sophisticated. The RAF defences were not just based on the combat power of Fighter Command. Just as important as the "teeth" of the defence was the "eyes and ears" – its nervous system which carried intelligence and information between them to position the "teeth" to strike.Price 2010, p. 37.

By the summer, 1940, the Chain Home radar stations along the English and Scottish coasts were able to track incoming aircraft from continental Europe at all but the lowest altitudes. The best detection altitude was . Aircraft at this height could be detected over away. To assess their identity, IFF (Identification Friend or Foe) could, by means of a distinctive blip on radar screens, distinguish German and British aircraft.Price 2010, p. 38.

The radar technology was not flawless. It struggled to gauge heights of incoming formations above and could not measure their numerical strength. It could also take several minutes to assess the line of advance for aircraft on a zigzag course. Moreover, the radar looked out to sea and was unable to track aircraft overland. That was the job of the Royal Observer Corps. Tens of thousands of volunteers, the length and breadth of Britain tracked the German formations over land. They were connected to Sector airfields by landline and could communicate intelligence in real time.

The detection and interception of incoming raids was as follows:
* Radar detects the enemy aircraft
* Radar plots are dispatched by landline to the filter room at Fighter Command Headquarters, Stanmore Park
* At the filter room enemy plots were compared with known plots of RAF fighters to assess identity to corroborate IFF
* Unidentified or hostile plots were dispatched by landline to fighter group or Sector operations rooms for plotting on situation maps
* No. 11 Groups operations room at RAF Uxbridge kept a record of the status of each unidentified or hostile raid, and the state of RAF Squadrons; whether they were refuelling, landing, in combat or scrambling
* Fighter controllers at the Sector operations rooms would choose which formations to engage and exactly what and how many Squadrons to scramble and issue the relevant orders to satellite controllers
* Fighter controllers at satellite fields would then bring their Squadrons into the field as directed by Sector controllers
* Squadrons would be loosely deployed across the south east to prevent the enemy slipping through
* Squadron Leaders are then responsible for the combat engagement

Anti-aircraft defences

Conventional defensive weapons included the anti-aircraft artillery piece. The three main types were the 4.5-inch, 3.7-inch and 3-inch guns. The first two were modern, and effective over . The last was a First World War weapon effective only to . Usually batteries were sited in fours, with a range-finder and predictor which measured the speeds and heights of enemy aircraft while taking into account the time shell took to reach their intended targets, thus calculating when to detonate the fuse in the shell.Price 2010, p. 52. As with most artillery weapons firing at aircraft, the higher the shell travelled the less effective it became. A shell fired to would only be half as effective at and a quarter as accurate at . The German bombers usually tried to fly around heavy concentrations of anti-aircraft guns, and if forced to fly through them, chose to fly at heights of around .Price 2010, p. 53.

Most of the heavy artillery defences were located around London and the Thames Estuary. Others were concentrated around Dover, Folkestone, Harwich, Ipswich, Portsmouth and Southampton docks.

For low-level defence, the Bofors 40 mm was used. This cannon had a rate of fire of 120 rounds a minute. The shells were capable of blowing a hole in an aircraft big enough for a man to fit through. However, there were only a few available and they were in short supply at RAF Kenley and Biggin Hill. To make up the difference 3 inch guns, firing over open sights from 1918 were used. They could fire only 15 rounds per minute.Price 2010, p. 50.

One unusual defensive weapon was in use at Kenley on 18 August; the parachute-and-cable. Located on the north side of the airfield at intervals, these were fired vertically by a rocket in salvoes of nine or more. As enemy aircraft came in at low-altitude, the parachute deployed and held a long steel cable from an altitude of . If struck by an aircraft, a second parachute deployed and tangled the device around the victim. If the cable was picked up on the wing, there was a good chance that the aircraft would go down out of control. This device had not been used before 18 August 1940.Price 2010, p. 51. Also available were barrage balloons with cutting cables capable of tearing off bombers' wings.

Lunchtime engagement

German build-up

The morning weather was clear and sunny, making ideal flying conditions. At his headquarters in Brussels, Albert Kesselring commanding ''Luftflotte 2'' (Air Fleet 2) directed the ''Geschwader'' (wings) under his command to carry out attacks on Biggin Hill and Kenley. KG 1 was to send 60 Heinkel He 111s from its base in Amiens to conduct a high-level attack on Biggin Hill. KG 76, based in airfields to the north of Paris, was to attack RAF Kenley. The ''Kampfgeschwader'' (bomber wing) could muster 48 Dornier Do 17s and Junkers Ju 88s. The force attacking Kenley was smaller numerically than the one hitting Biggin Hill and the Ju 88 and Do 17 carried only two-thirds the bomb-load of a He 111. The planners reasoned that a more accurate low-level strike carried out by a ''staffel'' from KG 76 would compensate for the weaker firepower of KG 76s main formations. Fighter escort was provided by ''Jagdgeschwader 3'' (JG 3), ''Jagdgeschwader 26'' (JG 26), ''Jagdgeschwader 51'' (JG 51), ''Jagdgeschwader 52'' (JG 52), ''Jagdgeschwader 54'' (JG 54) and ''Zerstörergeschwader 26'' (ZG 26). The ''Jagdgeschwader'' would carry out free-hunting and close escort from bases in the Pas-de-Calais.Price 2010, p. 61.

Both of the targeted airfields contained sector operations rooms from which the British fighters were directed into action. These airfields were selected by the Luftwaffe because they were the largest ones known to be operating RAF fighters. The German intelligence had no knowledge of the sector operations rooms there. The rooms were above ground and had little protection. If these buildings were to be hit, it would be a serious blow to the control system in the region.

At their airfield at Cormeilles-en-Vexin, ''9 Staffel'' (Squadron) KG 76 were briefed by their commander ''Hauptmann'' (Captain) Joachim Roth. The ''Staffel'' was to conduct a low-level attack against Kenley with Roth flying as a navigator in the lead aircraft. The unit had specialised in low-level attacks in France with great success. The nine Do 17s were to head across the Channel and make landfall at Beachy Head. From there they were to follow the Brighton–London rail line north-east to the target area. The crews were ordered to concentrate their attacks against buildings and hangars on the southern end of the airfield.Price 2010, p. 62.

The Dorniers were to carry twenty bombs each fitted with a fuse that would allow for function if released higher than ; the type of bomb previously used by the ''Staffel'' had to release from twice this height, making the unit's Do 17s correspondingly more vulnerable to ground fire.

The attack was to be part of a coordinated pincer movement against the airfields. Ju 88s from II./KG 76 were to dive-bomb buildings and hangars from high-altitude first. Five minutes later, 27 Do 17s from I. and II./KG 76 would level-bomb from high altitude to crater the runways and landing grounds while knocking out its defences. ''9 Staffel'' KG 76, the specialist low-level strike unit, would go in and finish off any buildings still standing. It was a bold and imaginative plan. If it worked, it would wreck Kenley from end-to-end. The high-flying bombers would have full fighter escort but the low-flying bombers would have to use stealth to avoid interception to and from the target area. The operation began at 09:00 but was postponed because of heavy haze reducing visibility up to 4,000 feet.

In the intervening time, a few skirmishes took place between RAF fighters and German reconnaissance aircraft. A ''Lehrgeschwader 2'' (LG 2) Bf 110 was shot down in the morning. At 11:00 1's formations took off and the main formations headed out to sea. The form-up was more difficult for KG 76 and its Do 17s and Ju 88s. Their bases in and around Calais were covered in 8/10ths cloud cover with a base of 6,500 feet which reached to 10,000 feet. As the bombers climbed through the haze the formation soon lost cohesion. Valuable time was lost as they reformed. The Do 17s of I. and III./KG 76 had overtaken the III./KG 76 Ju 88s which should have been ahead of them by five minutes. These delays had serious consequences for ''9 Staffel'' KG 76.Price 2010, p. 65.

Meanwhile, Gerhard Schöpfel, leading III./JG 26 and Bf 109s from JG 3, 40 in total, were already crossing the Dover straits to sweep the skies clear ahead of the main raid. Some 25 miles behind him were the 27 Do 17s of I. and III./KG 76 escorted by 20 Bf 110s that were to strike Kenley. Close by the Dorniers were the Ju 88s of III./KG 76 escorted by Bf 109s from JG 51. This formation should have been 15 miles in front. Some 15 miles to the rear of the Ju 88s, KG 1's He 111s were bound for Biggin Hill, escorted by 40 Bf 109s from JG 54. The formations were moving at around three miles per minute, at 12,000 feet. Around 50 miles to the south-west, the nine Do 17s of ''9 Staffel'' were at wave-top height, halfway between Dieppe, Seine-Maritime and Beachy Head, intent on sneaking under British radar beams unobserved. Altogether, the raiding force contained 108 bombers and 150 fighters.Price 2010, p. 66.

British scramble

The British followed the main raids and were aware of all the approaching aircraft, save for the low-altitude ''9 Staffel''. The radar station near Dover began reporting a build-up over the Pas-de-Calais area. This activity increased until 12:45 when six separate concentrations were reported. The plotters estimated the strength of the force as 350 aircraft, one-third more than the actual size.Price 2010, p. 66.

At RAF Uxbridge, AOC No. 11 Group RAF Keith Park and his controllers directed No. 501 Squadron RAF and its 12 Hawker Hurricanes, already in the air, to Canterbury at 20,000 feet. They had been on their way back to RAF Gravesend having spent most of the morning on patrol operating from RAF Hawkinge near Folkestone. Within minutes eight more Squadrons were dispatched to meet them; two from Kenley, two from Biggin Hill and one each from North Weald, Martlesham Heath, Manston and Rochford.

Within a short time the fighters assigned to engage were all airborne. Five Squadrons; No. 17, No. 54, No. 56, No. 65, and 501 with 17 Supermarine Spitfires and 36 Hurricanes were moving to patrol the Canterbury-Margate line to block any attack on the Thames Estuary ports or the airfields to the north of it. Four Squadrons; No. 32, No. 64, No. 601, and No. 615, with 23 Spitfires and 27 Hurricanes went into position above Kenley and Biggin Hill. A total of 97 RAF fighters were to meet the attack.Price 2010, p. 67.

Park did not send all of his forces aloft, and he held a reserve. Three Squadrons at RAF Tangmere were kept and made ready to meet more attacks from the south. Six more were in reserve to meet a possible follow-up to the coming raid.Price 2010, p. 68.

''9 Staffel'' KG 76 attacks Kenley

As the advance led by Gerhard Schöpfel made their way past the coast it spotted the vic-formation of RAF fighters. They were Hurricanes of 501 Squadron which were conducting wide spirals to gain height. Schöpfel bounced them and shot down four in two minutes killing one pilot and wounding three others. As he departed other members of his ''Geschwader'' (Wing) dived on the Squadron and an inconclusive dogfight ensued. Schöpfel's victims were Donald McKay and Pilot Officers J.W Bland, Kenneth Lee and F. Kozlowski. Bland was the only one killed.

Both the Do 17s and Ju 88s of the III./KG 76 encountered flak as they crossed Dover. The Do 17s were escorted by ZG 26 while III./JG 51 led by Hannes Trautloft escorted the Ju 88s. The German bombers had flown east of Canterbury and thereby avoided the main concentration of fighters on the Canterbury-Margate line. At 13:01 they passed over Ashford and had a clear run before they reached Biggin Hill and its four defending squadrons.

As ''9 Staffel'' crossed the coast they were fired at by Royal Navy patrol boats. The machine gun fire was ineffective. However, the Royal Observer Corps Post K3, situated on top of Beachy Head, spotted the Dorniers. They immediately telephoned a warning to Observer Group Headquarters at Horsham and fighter sector stations in the area, including RAF Kenley. Wing Commander Thomas Prickman, the station commander at Kenley, noticed the low-flying Dornier plot appear on his situation map. They appeared to be heading away towards the west, and Prickman was unsure of their target. His controllers were organising Nos. 64 and 615 Squadrons to meet the high-altitude raid. Roth headed past Lewes until he picked up the Brighton–London rail line. He then turned north-west.Price 2010, pp. 72–73.

With the Observer Corps passing a steady stream of reports regarding approaching German formations they soon realised a coordinated attack was under way. The two Squadrons approaching the high-altitude attack could not be diverted and no fighters had been asked to engage the ''9 Staffel''. The only Squadron on the ground in the area was No. 111 Squadron RAF that had 12 Hurricanes at RAF Croydon. Although usually the responsibility of Park, the controllers took the matter into their own hands and ordered all aircraft into the air. Even those that were not in combat condition were flown north-east, to avoid them being caught on the ground.Price 2010, pp. 74–75.

No. 111 Squadron managed to get into position above Kenley at 3,000 feet. With luck they could intercept ''9 Staffel''. Biggin Hill soon took the same precaution of ordering all fighters into the air by order of Group Captain Richard Grice. At 13:10 the German bombers were within 40 miles of the BBC
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