“Absence of rudder trimmer is a bad feature, although at low speeds the practical consequences are not so alarming as the curves might suggest, since the rudder is fairly light on the climb. At high speeds, however, the pilot is seriously inconvenienced, as above 300 mph about 2 1/2 degrees of port (left) rudder are needed for flight with no sideslip and a very heavy foot load is needed to keep this on. In consequence the pilot’s left foot becomes tired, and this affects his ability to put on left rudder in order to assist a turn to port (left). Hence at high speeds the Bf.109E turns far more readily to the right than to the left.”
— RAF Royal Aircraft Establishment (RAE) Farnborough handling trials,Bf.109E Wn: 1304. M.B. Morgan and R. Smelt of the RAE, 1944.
Speed – The top speed of 348 mph is very good for an early war fighter.
Climb Rate – The Bf-109s all had superior climb rate over their competition up to 20,000 feet.
Ammo Load – Although the firepower is greatly increased by addition of the MG-FF/M cannon, their ammo load of only 60 rpg is used up in less than 10 seconds of fire time, leaving just a pair of 7.9mm machine guns.
Durability – The 109 was a small plane and not capable of absorbing much combat damage.
During the fall of 1939, Luftwaffe front-line units started to receive the new Bf-109E-3 model equipped with a pair of 20mm MG-FF cannon with 60 rpg in place of the MG-17s in the wings. In addition to the upgraded armament, the 1,175 hp DB-601Aa was installed, boosting top speed from 334 to 348 mph.
A pair of E-3s fell into French hands in early May 1940 and, after examination by the French Air Force, were shipped to England on May 14 for trials and evaluations. The lessons learned about the performance of the Spitfire versus the Messerschmitt enabled the RAF to employ improvements to their fleet in time for the Battle of Britain and influenced future development.
During the French campaign, several lessons were learned and the E-4 model was intended to incorporate these improvements. In addition to increasing the pilot’s armor protection by about 75 lbs., the new MG-FF/M cannon, which employed a more powerful “mine” shell, were mounted in place of the older models.
Additionally, experiments were made with mounting a rudimentary bomb rack on E-3s in combat. This proved successful enough that a bomb rack was mounted on the special E-4/B model at the factory, which was used to equip Erpobungsgruppe 210 for field testing. In addition to bombs, the rack could carry a 300 liter drop tank, thus increasing the range of the fighter.
The E-5 and E-6 models were reconnaissance versions of the E-4, but the E-7 was a fighter variant which incorporated the bomb and drop tank carrying capacity of the E-4/B into the main production run, thus giving all planes the same capability.
The E-4 was the first variant to be “tropicalized” for use in the Western Desert. The conversion consisted of adding a dust filter to the supercharger air intake and installing an emergency desert survival kit in the cargo space of the fuselage, which even included a carbine for personal protection.