Short answers, pulled from the story.
Winston Churchill declared that the Battle of Britain was about to begin on the 18th of June, 1940. This speech gave the campaign its name before a single shot had been fired in anger.
The DB 601 engine used fuel injection allowing vertical-plane negative-g maneuvers without cutting out while carburettor-equipped Merlin engines could not perform this trick as readily. The Messerschmitt Bf 109E flew up to 40 mph faster at certain altitudes but British squadrons gained approximately 30 mph by converting to 100 octane fuel by mid-1940.
This system maintained an average interception rate of over 75% during the battle compared to early war missions having only a 30% chance of ever seeing their target. Reports flowed from observation posts directly to Fighter Command Headquarters at Bentley Priory where operators filtered multiple reports into single tracks before forwarding them to Group headquarters.
Abteilung V produced a report on the 16th of July, 1940 that lacked information on RAF radar capabilities and assumed the British system was rigid and inflexible with fighters tied to home bases. Oberstleutnant Beppo Schmid led this intelligence unit which assessed Fighter Command strengths incorrectly leading to an optimistic conclusion that the RAF would run out of frontline fighters quickly.
No. 303 Polish Fighter Squadron became the highest-scoring unit even though it joined two months late. One hundred forty-five Poles served in the Royal Air Force during the conflict while about 20% of all pilots who took part came from non-British countries.