Adlertag ("Eagle Day") was the first day of Unternehmen Adlerangriff ("Operation Eagle Attack"), an operation by Nazi Germany's Luftwaffe (air force) intended to destroy the British Royal Air Force (RAF). The operation came during the Battle of Britain after Britain rejected all overtures for a negotiated peace with Germany. However, Adlertag and subsequent operations failed to destroy the RAF or gain local air superiority.
On 16 July 1940 Hitler gave the German armed forces (Wehrmacht) Directive No. 16 ordering provisional preparations for the invasion of Britain. This operation was codenamed Operation Sea Lion (Unternehmen Seelöwe). Before this could be carried out, air superiority or supremacy was required. The Luftwaffe was to destroy the RAF in order to prevent it from attacking the invasion fleet or providing protection for the Royal Navy's Home Fleet, which might attempt to prevent a landing by sea. On 1 August Hitler gave the Luftwaffe's commander-in-chief, Reichsmarschall Hermann Göring and the Oberkommando der Luftwaffe Directive No. 17 —"For the conduct of air and sea warfare against England"— to launch the air assault.
The essential target was RAF Fighter Command. The service's destruction would deny the British their air superiority asset and feeling vulnerable to air attack might negotiate for peace. Throughout July and early August, the Germans made preparations for Adlertag. The date of the assault was postponed several times because of bad weather. Eventually it was carried out on 13 August 1940, inflicting significant damage and casualties on the ground, but, marred by poor intelligence and communication, they did not significantly impair Fighter Command's ability to defend British air space.
Göring had promised Hitler that Adlertag and Adlerangriff would achieve the results required within days, or at worst weeks. It was meant to be the beginning of the end of RAF Fighter Command, but Adlertag and the following operations failed to destroy the RAF, or gain the necessary local air superiority. As a result, Operation Sea Lion was postponed indefinitely.
Background
Strategic overview
After the declaration of war on Nazi Germany by Britain and France in the aftermath of the German invasion of Poland, nine months of stalemate took place along the Western Front. After the Polish Campaign, in October 1939, the planners of the Oberkommando der Luftwaffe (OKL – Luftwaffe (Air Force) High Command) and the Oberkommando der Wehrmacht (OKW – Supreme Command of the Armed Forces) turned their attentions to Western Europe.
The German offensive—named Unternehmen Gelb (Operation Yellow), also known as the Manstein Plan—began in the west on 10 May 1940. The central campaign—the Battle of France—ended in Allied defeat and the destruction of the main French Army forces. The British Expeditionary Force escaped encirclement during the Battle of Dunkirk, but the Wehrmacht captured Paris on 14 June and overran half of France. The French surrendered on 25 June 1940.
With Western Europe neutralised, the OKL and OKW turned their attention to Britain, which was now home to the Allied base of operations in Europe. Hitler hoped Britain would negotiate for an armistice, for which he was prepared to offer generous terms. The tentative offers made by Hitler were rejected by the Churchill coalition government. Hitler now ordered the Luftwaffe and Kriegsmarine to prepare for an amphibious assault of Britain, codenamed Operation Sealion. The Luftwaffe was to eliminate enemy air power and the Kriegsmarine was ordered to make all the necessary preparations for transporting the German army (Heer) across the English Channel. The Luftwaffe's task came first. Once the RAF had been rendered impotent, Göring and Hitler hoped that an invasion would be unnecessary. If this proved not to be the case, the Luftwaffe would then support the army and prevent the Royal Navy interdicting German sea traffic. Göring named the offensive against the RAF as Operation Eagle Attack (Adlerangriff).
Background: early battles
The losses of the spring campaign had weakened the Luftwaffe before the Battle of Britain. Over 1,400 aircraft had been lost in the Battle of France on top of about 500 lost in conquering Poland in 1939 and Norway in 1940. The service was forced to wait until it had reached acceptable levels before a main assault against the RAF could be made.
Therefore, the first phase of the German air offensive took place over the English Channel. The Kanalkampf ("Channel battle") rarely involved attacks against RAF airfields inland, but encouraged RAF units to engage in battle by attacking British Channel convoys. These operations would last from 10 July to 8 August 1940. The attacks against shipping were not successful; only 24,000 tons (gross register) was sunk. Minelaying from aircraft 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, and its strength rose to 1,429 by 3 August. By that date, it was short only 124 pilots.
In the second phase of attacks, shipping, coastal airfields, radar and stations south of London were attacked during 8–18 August. The Luftwaffe gradually increased the frequency of attacks. German bombers also raided targets as far north as Liverpool during night hours.
By 12 August, German air strength had reached acceptable levels. After bringing its serviceable rates up, the Luftwaffe began Adlertag with 71 percent of its bomber force, 85 percent of its Bf 109 units, and 83 percent of its Bf 110 units operational.
The first major raid inland and against RAF airfields came on 12 August. RAF Hawkinge, Lympne, Manston and radar stations at Pevensey, Rye and Dover were to be destroyed. Portsmouth docks were also targeted. The results of the raids were mixed. The radar station at Ventnor was badly damaged and others targeted were also damaged, but not destroyed. All but Ventnor were in working order by the following morning. Attacks against the harbour and RAF stations failed to destroy them. Though none were in full working order at the end of the day, all were back in action the following morning. Unknown to German intelligence, Lympne itself was not even an operational station. This sort of intelligence blunder contributed to the failure of Adlertag.
Overall, the Germans had not achieved a degree of success commensurate with their exertions.
Luftwaffe preparations
Intelligence
Faulty intelligence was the component that was mostly responsible for the failure of Adlertag. While the gap between the British and Germans was not yet wide in this regard, the British were starting to gain a decisive lead in intelligence. The breaking of the Enigma machine and poor Luftwaffe signals discipline allowed the British easy access to German communications traffic. The impact of Ultra on the Battle of Britain is a matter of dispute, with Official Histories claiming there was no direct impact. Whatever the truth, Ultra, and the Y service in particular, gave the British an increasingly accurate picture of German order of battle deployments.
Joseph "Beppo" Schmid was commander of the Luftwaffe's Military Intelligence Branch (Abteilung 5 as Chief IC). Throughout this time, Schmid's reports made a series of errors. In July 1940, Schmid grossly overestimated the strengths of the Luftwaffe and underestimated the RAF. The most serious mistakes were made concerning radar, airfield identification, and production sites. Schmid asserted that the number of operational airfields in southern England were severely limited; estimated that the British could produce only 180–330 fighters per month (the true figure was 496) and that figure would decrease, indicating that the RAF could not sustain a long battle of attrition. Schmid also claimed the command at all levels was rigid and inflexible, with fighters being tied to home bases. In his list of omissions, Schmid failed to mention the RAF maintenance and organisation operations, which put back damaged aircraft with rapid effect. He anticipated a short battle. Crucially, Schmid failed to mention radar at all.
The lack of sustained and concentrated attacks on radar left it free to help direct the deployment of RAF units at opportune moments. Its continued warnings of incoming raids were a crucial benefit to Fighter Command. The Luftwaffe also had poor intelligence on the type of RAF airfields. It made repeated errors, often misidentifying airfields as Fighter Command bases, which turned out to belong to RAF Coastal Command and RAF Bomber Command. On Adlertag, most of the targets on the Luftwaffe's list—if destroyed—would not have impaired Fighter Command in the slightest.
Targets and order of battle
The following targets were chosen for attack on 13 August 1940:
RAF operational command
The keystone of the British defence was the complex infrastructure of detection, command, and control that ran the battle. This was the Dowding System, after its chief architect, Air Chief Marshal Sir Hugh Dowding, the air officer commanding RAF Fighter Command. Dowding modernised a system created up from 1917 by Major General E B Ashmore. The core of Dowding's system was implemented by Dowding himself: the use of Radio Direction Finding (RDF or radar) was at his behest, and its use, supplemented by information by the Royal Observer Corps (ROC), combined with an organisation system to process the information was crucial to the RAF's ability to efficiently intercept incoming enemy aircraft. The technology was named RDF with misleading intent – the vague description would disguise the full nature of the system to the enemy if its existence ever became known.
The first indications of incoming air raids were received by the Chain Home RDF facilities, which were located along the coastlines of Britain. In most circumstances, RDF could pick up formations of Luftwaffe aircraft as they organised over their own airfields in northern France and Belgium. Once the raiding aircraft moved inland behind the radar stations, the formations were plotted by the ROC. The information from RDF and the Observer Corps were sent through to the main operations room of Fighter Command Headquarters at RAF Bentley Priory. The plots were assessed to determine whether they were "hostile" or "friendly". If hostile, the information was sent to the main "operations room", which was in a large underground bunker.
Here, the course information of each raid was plotted by Women's Auxiliary Air Force (WAAF), who received information by telephone. Additional intelligence was provided by the Y Service radio posts, which monitored enemy radio communications, and the Ultra decoding centre based at Bletchley Park, which gave the RAF intelligence on the German order of battle. Colour-coded counters representing each raid were placed on a large table, which had a map of Britain overlaid and squared off with a British Modified Grid. As the plots of the raiding aircraft moved, the counters were pushed across the map by magnetic "rakes". This system enabled the main "Fighter Controller" and Dowding to see where each formation was heading, at what height, and in what strength. This allowed an estimate to be made of possible targets. The age of the information was denoted by the colour of the counter. The simplicity of the system meant that decisions could be made quickly.
This information was simultaneously sent to the headquarters of each group, where it was cross-checked through a filter room before being sent through to another operations room, housed in an underground bunker. Because Group had tactical control of the battle, the operations room was different in layout from the main headquarters at Bentley Priory. The main map on the plotting table represented the group command area and its associated airfields. Extensive radio and telephone equipment transmitted and received a constant flow of information from the various sector airfields as well as the Observer Corps, AA Command and the navy. The "Duty fighter controller" was the Group GOC's personal representative and was tasked with controlling how and when each raid would be intercepted. If the telephone system failed engineers would be on site within minutes to repair the broken links.
Battle
KG 2 raid
On the morning of 13 August, the weather was bad and Göring ordered a postponement of raids. However, the Dornier Do 17s of KG 2 were not informed and took off at 04:50 for their target. They were to meet with their escorts from ZG 26 over the Channel. ZG 26 received the cancellation order, but II., and III./KG 2 did not. KG 2 had formed up by 05:10, led by Geschwaderkommodore Johannes Fink. Part of the ZG 26 formation that had taken off—led by Oberstleutnant Joachim Huth—tried to warn the Dorniers of the cancellation. Unable to contact the bombers by radio, Huth tried to signal them by flying in front of them and performing aerobatics. Fink ignored him and flew on. KG 2 flew around the coast to its target, Eastchurch airfield on the Isle of Sheppey. Albert Kesselring had issued orders for bombers to abandon missions if their escorts did not show up, but Fink did not want to be accused of failing to obey orders and continued onward even though the Bf 110s turned back. The return leg would take KG 2 across No. 11 Group's territory, which could have been disastrous without fighter escort but owing to the Observer Corps misjudging the direction of the bombers, due to low-lying cloud, and the radar not picking up the direction of the German bombers, the WAAF plotted the course of the raid incorrectly and the RAF failed to prevent the target being attacked.