The Messerschmitt Bf-109K was the last model developed of the Bf-109. The K series was the result of a decision to standardise all modifications and improvements that had been made up until that time, as well as introducing some new features, such as a new instrument panel layout and moving the oxygen apparatus from the fuselage to the right wing. Work on the new version began in 1943, and the prototype was ready by the autumn of that year, with series production starting in August 1944. Operational service began in October 1944, and that month alone some 200 aircraft were delivered to the frontline units. By the end of January 1945, despite heavy bombing and advances by the Allies, over 300 K-4s - about every 4th 109 - were operational with the frontline Luftwaffe units.
The Bf 109 K-4 was the fastest 109 of WWII, acheiving some 715 km/h (445 mph) at 7,500 m altitude; improved propellers were being developed when the war ended which increased the speed to 727 km/h (452 mph). Rate of climb was outstanding, up to 5,500 ft/min at 1.8ata.
The Messerschmitt Bf-109K-4 was a remarkable aircraft, and remained comparable to the highest performing Allied or Soviet fighters until the end of the War.
Approximately 1,700 K models were delivered by factories before the end of hostilities.