Messerschmitt Bf.109E - German users, part one *Battle of Britain special*

The most famous aerial operation of the Bf.109E was the contest of aerial superiority over the skies of England, between the Royal Air Force and the Luftwaffe during the summer 1940.
Most of German fighter units at the time were already equipped with the Bf.109E-3 and E-4.
As a matter of fact, on 31st August 1940, all fighter units, excluding JG.77, reported to have 375 E-1s, 125 E-3s, 339 E-4s and 32 E-7s, so the E-3s were already under conversion towards the E-4. By july 1940, a fighter group, JG 26, was equipped with the Bf.109E-4/N with improved performance, powered by the new DB 601N using the 100 octane aviation fuel.
That fuel injected variant proved to be very useful against British Supermarine Spitfire and Hawker Hurricane, the backbone of the RAF during the Battle of Britain, as their British counterparts used gravity-fed carburetted engines that tended to cut-out at negative G-forces when the DB 601N didn't. Therefore the Bf.109E had the advantage when diving as it could blunt directly into a dive without loss of power. Regarding the armament, the British ones were armed with eight 7.7mm (0.303in) machine guns whereas most of the E variants were armed with two 7.92mm (0.312in) and two 20mm MGFF cannons. These late ones, fired many types of ammunitions, among them high-explosive shells, but with different ballistic properties to the MG17 as the MGFF were short on rounds, 60 rounds, making some aircraft to be fixed only with the MG17 as it could carry more ammo.
In August 1940 the Luftwaffe tested the Bf.109 against the Spitfire at Rechlin test centre being Werner Mölders (the leading Luftwaffe ace at the time) one of the participants. They concluded that the Bf.109 had better level and climbing speed to the Spitfire and Hurricane at all altittudes but the British ones had smaller turning circle. Therefore, the Luftwaffe advised their pilots to not engage the Spitfire or the Hurricane in turning dogfights unless they could use the Bf.109E in its full potential. Roll rate of the Bf.109E was also considered superior, as well as its stability on target approach.
During the Battle of Britain, the main disadvantage of the Bf.109E was its short range. As almost every monoplane designed in the 1930s, it was designed to intercept enemy bombers over friendly territory, so it wasn't foreseen the need to escort bombers over enemy territory. So Bf.109E used as escorts, had a maximum range of 660Km (410Milles) just on internal fuel and when arriving on British territory they had only an autonomy of 10 minutes, before having to turn for home, leaving bombers unescorted. This disadvantage, wasn't solved until the Focke-Wulf 190A came out, which by the summer 1940 was still in prototype form. The Bf.109E-7 issued this flaw by adding a ventral central-line where either an external fuel tank or bombs could be fitted. If the 300L was fitted the range increased to 1325Km (820 Milles) but the central rack wasn't retrofitted in the earlier models until October 1940. The Spitfire and Hurricanes, as they operated on their homeland, they could stay on the air much longer, as they flew over their airfields and bases.

Sources:
1. https://en.wikipedia.org/wiki/Messerschmitt_Bf_109_operational_history#Combat_service_with_the_Luftwaffe
2. Salamander Books - The Complete Book of Fighters
3. Signal Squadron - Aircraft In action  44 - Messerschmitt Bf-109 in Action Pt.1