Germany Begins Main Assault on English Coastal Airfields
The main attack upon the RAF's defences was code-named Adlerangriff ("Eagle Attack"). Weather, which proved an important feature of the campaign, delayed Adlertag, ("Eagle Day") until 13 August 1940.
On 12 August, the first attempt was made to blind the Dowding system when aircraft from the specialist fighter-bomber unit, Erprobungsgruppe 210 attacked four radar stations. Three were briefly taken off the air but were back working within six hours. The raids appeared to show that British radars were difficult to knock out for any length of time. The failure to mount follow-up attacks allowed the RAF to get the stations back on the air, and the Luftwaffe neglected strikes on the supporting infrastructure, such as phone lines or power stations, which could have rendered the radars useless, even if the towers themselves (which were very difficult to destroy) remained intact.
Adlertag opened with a series of attacks, led again by Epro 210, on coastal airfields used as forward landing grounds for the RAF fighters, as well as 'satellite airfields' (including Manston and Hawkinge). As the week drew on, the airfield attacks moved further inland, and repeated raids were made on the radar chain. 15 August was "The Greatest Day" when the Luftwaffe mounted the largest number of sorties of the campaign. Luftflotte 5 attacked the north of England. Believing Fighter Command strength to be concentrated in the south, raiding forces from Denmark and Norway ran into unexpectedly strong resistance. Inadequately escorted by Bf 110s, bombers were shot down in large numbers. As a result of the casualties, Luftflotte 5 did not appear in strength again in the campaign.
18 August, which had the greatest number of casualties to both sides, has been dubbed "The Hardest Day". Following the grinding battles of 18 August, exhaustion and the weather reduced operations for most of a week, allowing the Luftwaffe to review their performance. "The Hardest Day" had sounded the end for the Ju 87 in the campaign. This veteran of Blitzkrieg was too vulnerable to fighters to operate over Britain, and to preserve the Stuka force, Göring withdrew them from the fighting. This removed the main Luftwaffe precision-bombing weapon and shifted the burden of pinpoint attacks on the already-stretched Erpro 210. The Bf 110 had also proven too clumsy for dogfighting with single-engined fighters, and its participation was scaled back. It would only be used when range required it or when sufficient single-engined escort could not be provided for the bombers.
Göring made yet another fateful decision: to order more bomber escorts at the expense of free-hunting sweeps. To achieve this, the weight of the attack now fell on Luftflotte 2, and the bulk of the Bf 109s in Luftflotte 3 were transferred to Kesselring's command, reinforcing the fighter bases in the Pas-de-Calais. Stripped of its fighters, Luftflotte 3 would concentrate on the night bombing campaign. Göring, expressing disappointment with the fighter performance thus far in the campaign, also made a large change in the command structure of the fighter units, replacing many Geschwaderkommodore with younger, more aggressive pilots like Adolf Galland and Werner Mölders.
Finally, Göring stopped the attacks on the radar chain. These were seen as unsuccessful, and neither the Reichsmarschall nor his subordinates realised how vital the Chain Home stations were to the defence. It was known that radar provided some early warning of raids, but the belief among German fighter pilots was that anything bringing up the "Tommies" to fight was to be encouraged.
Thus a plan was hatched to directly attack the RAF airfields and aircraft production centers, Hermann Göring called his plans Adlerangriff (Eagle Attack), beginning on August 11 with Adlertag (Eagle Day). But even before this there was to be a month of attacks on Channel convoys and the RAF out over the water. This period of fighting was called Kanalkampf by the Germans.
The British were fully aware of the German goals, strategy, and often even tactics due to their ability to read the German Enigma cypher, which was used for most high-security German military radio communications. This fact, not revealed until the 1970s, was crucial in forming British tactics. They had also killed or turned all German agents in Britain.