from wikipedia
The Kanalkampf (Channel fight) was the German term for air operations by the Luftwaffe against the British Royal Air Force (RAF) over the English Channel in July 1940. The air operations over the channel began the Battle of Britain. By 25 June, the Allies had been defeated in Western Europe and Scandinavia. Britain rejected peace overtures and on 16 July, Adolf Hitler issued Directive 16 to the Wehrmacht (German armed forces), ordering preparations for the invasion of Britain, under the codename *Unternehmen Seelöwe Operation Sea Lion
The Germans needed air superiority over southern England before the invasion and the Luftwaffe was to destroy the RAF, assume command of the skies and protect the cross-channel invasion from the Royal Navy. To engage RAF Fighter Command , the Luftwaffe attacked convoys in the English Channel. There is some dispute among historians about the dates for the beginning and end of the battle and British histories usually treat 10 July as the beginning. British and German writers and historians acknowledge that air battles were fought over the Channel between the Battle of France and Britain; deliberate German attacks against British coastal targets and convoys began on 4 July. During the Kanalkampf , the Luftwaffe received modest support from shore artillery and the E-Boats of the Kriegsmarine (German navy).
Operations against British sea communications did not appeal to Reichsmarschall Hermann Göring. In Göring’s view, the Luftwaffe was not prepared for naval warfare and this strategy was tantamount to Blockade which was put in effect against Britain from 18 July, required the co-operation of the Luftwaffe with the Kriegsmarine. Göring ensured air assistance was not forthcoming Göring loathed the navy and its Commander-in-Chief Großadmiral Erich Raeder. In Göring’s eyes, both Raeder and the navy represented the bourgeois clique of German society the National Socialist revolution had pledged to eliminate. Cooperation would not be easy and the Reichsmarschall consistently refused to accept the navy’s calls for assistance in the war against the Royal Navy and British commerce throughout the conflict. All of the directives issued to the Luftwaffe at this time, by the Oberkommando der Luftwaffe (OKL—High Command of the Air Force) or Oberkommando der Wehrmacht (OKW—Supreme High Command of the Armed Forces), expressly stated that sea attacks on warships and shipping must take second place to “military objectives.” The OKW did not alter this view until February 1941.
The campaign did not start against the RAF until August. Throughout the intervening period, the Luftwaffe undertook its third major operational move within the space of two months. The first had seen it push forward its Air Fleets into the Low Countries and the second into southern France. Now it was expanded into northern France and Belgium, along the English Channel coast. It took time to establish the signal system in France owing to a shortage of trained staff officers while the units replenished after losses through the Ergänzungsverbände (supplemental formations).
The logistics challenge was also evident in the lethargic build up. Matters were not helped by the fact that the Luftwaffe and army had to repair the French and Belgian infrastructure which had been badly damaged during the Battle of France. The army was forced to rebuild bridges to supply forward bases. Air bases also required rebuilding after war damage in May and June. This often meant short-range dive bombers and fighters were sent to forward airfields which were urgently in need of electricity and running water for personnel.
Upon the French surrender the Luftwaffe supply system was breaking down. For example, on 8 July only 20 of the 84 railway tanks with aviation fuel had reached the main depot at Le Mans. The Transportgruppen (transport groups) could not cope and barely kept their own units running. Preparations continued at a glacial pace, since the men responsible for the organisation of German air power and its efficient transfer to the Channel, were enjoying the fruits of their new assignments in Paris. Senior staff members were distracted by victory parades and promotions, including Göring who was promoted to Reichsmarschall . During the Kanalkampf the Germans assembled powerful air forces to attack convoys in the Channel but it took about forty days after the French capitulation, for the Luftwaffe to begin its assault on the Britain.
While many Luftwaffe units returned to Germany to replace losses, Luftflotte 2 and Luftflotte 3 sent small numbers of bombers against British sea communications, attacking ships and laying mines. In July, the Luftwaffe transferred air units to the European coast from Hamburg to Brest in Brittany on the French Atlantic coast.
Still RAF Fighter Command could not always protect adequately the convoys; Relations between the Air Ministry, War Office and the Admiralty had been strained since the independence of the RAF on 1 April 1918. In the early 1920s, the three services competed for resources, influence and the right of the RAF to exist as a separate service. The War Office and the Navy tried to abolish the RAF and regain control of army and naval aviation. By 1940, service rivalry had diminished but the Air Ministry remained suspicious of the intentions of the other services.
Cooperation was hindered by Fighter Command retaining rigid control of its units. The Admiralty complained that RAF methods did not permit direct contact by RAF operational staff liaising with the naval command. Time was lost and the fluidity of aerial warfare, meant that RAF aircraft came into action at the wrong time or place, often in numbers too small to defend the ships. Vice Admiral Max Horton the Commander-in-Chief Dover, responsible for organising the evacuation (Operation Dynamo), asked to meet Dowding in late June, to prevent the operational difficulties occurring again. Horton was told to put his complaints on paper and send them to Dowding, with a copy to the Air Ministry and they never met. It was felt by the Admiralty that the RAF was fighting a separate war, with little consideration given to joint operations.
The protection of shipping was a source of controversy in the RAF, since it required a substantial commitment of fighters. On average the 12 convoys passing through the Channel waters needed cover every day and roughly one-third were attacked. It became an immediate burden to No. 11 Group RAF under the command of Keith Park which was responsible for defending south-west England. The employment of convoys from the Suffolk coast to Lyme Bay negated the value of using the sea as a protective shield because the location gave tactical advantages to the attacker. Coastal radar could give little advance warning of incoming raids since the proximity of Luftwaffe airbases, meant that German aircraft could attack and quickly withdraw, making interception difficult. Standing patrols over convoys could compensate but this exhausted pilots and handed the tactical initiative to the Germans. On 9 August Winston Churchill was still asking the navy to use the convoys as bait to lure German bombers; the tactic succeeded but fighting over the sea caused Fighter Command greater losses.
As a result during attacks on numerous coastal convoys like Bread (10 July) , Booty , Agent , Bosom , Bacon , Peewit (7-8 August) the Germans sank several British and neutral ships and shot down a considerable number of British fighters. The Royal Navy was forced to suspend the sailing of large convoys in Channel waters during daylight and close it to ocean-going vessels until more protection could be arranged, which took several weeks. The Germans viewed temporary British naval withdrawal and brief suspension of merchant traffic as a success but the lack of targets for the Germans, eliminated the need for Fighter Command to engage the Luftwaffe over the Channel. The Germans now had to fly into southern England, which put the Bf 109, the best German fighter, at the limit of its endurance. Although British shipping losses in coastal routes were serious (Stephen Roskill, the Royal Navy official historian, wrote in 1957, that the operations were costly for both sides; had the RAF failed to increase the convoy protection effort, the route would probably have been abandoned) , considering that four million tons of shipping passed through British ports during this period , it was very little.
On 1 August, Hitler issued Directive 17, extending Luftwaffe operations to the British mainland and RAF-related targets and on Adlertag (Eagle Day, 13 August) the main air offensive against the RAF began. The Kanalkampf had drawn out Fighter Command as intended and convoy attacks continued for several more days. Both sides had suffered losses but the Luftwaff failed to inflict a decisive defeat on Fighter Command and the RAF; the Luftwaffe had yet to gain air superiority for Operation Sea Lion. (Luftwaffe commanders not realisaing Kriegsmarine neither had enough shipping tonnage , shipping or sealift capacity nor had an harmonious planning cooperation with German Army)
Between 4th July 1940 - 09 August RAF lost 115 fighters shot down over Channel with 75 pilots killed or lost. Merchant marine lost 35 ships sunk totalling 28.000 tons. Four Royal Navy destroyers and seven trawlers were sunk. 176 sailors killed.
Meanwhile Luftwaffe lost 215 aircraft over Channel (80 fighters rest bombers) , 478 airmen killed or missing , 16 airmen captured. Four E-Boats (fast torpedo attack boats) of German Navy were also sunk or damaged during this period , 36 German naval personnel killed.