Messerschmitt Bf.109K

The Bf.109K was the last operative variant to see action and the end of the Bf.109 evolutionary line. The K series came as an answer to the many series, models, modification kits and factory conversions for the Bf.109, which made the production and maintenance complicated and costly, and Germany barely could afford it late in the war. Therefore, the RLM ordered Messerschmitt to rationalize the production of Bf.109 by consolidating parts and types to produce a standard model with more interchangeable parts and equipment fixing also flaws in the airframe. Work on that new version began in spring 1943 and by autumn of that same year, the first prototype was already flying. However, as they encountered some design delays with the DB 605D engine, it wasn't until August 1944 that its mass production started. Initially, the K-4 version was the only one to be mass produced.
It could be identified by the position of the radio equipment hatch which was moved forward to a higher position between frames four and five and the filler point for the fuselage fuel tank, which was also moved forward between ribs two and three. The D/F loop was moved aft as well to sit between frames three and four on the fuselage spine and a small circular plate above the footstep on the port side was deleted. Rudder was fitted with a Flettner tab and two fixed tabs although some examples had any tabs at all. All the K-4s were fitted with completely retractable landing gear.
The wings featured big rectangular fairings for the large main wheels and wheel doors (originally planned for the G series) which completely covered them when retracted. However, they were oftenly removed in frontline units. It was equipped with a FuG 16ZY with the relocated main swept forward radio antenna under the port wing from the G-10 being carried through as the standard for the K-series airframes. They were also fitted with FuG 25a Erstling IFF system as well as the FuG 125 Hermine D/F equipment. Internally oxygen tanks were rellocated from the fuselage to the right wing.
It was armed with a 30mm Mk.108 motorkanone and two 13mm MG 131 in the nose. The 30mm motorkanone gave some problems as they oftenly jammed while the aircraft was maneouvering in battle, leaving the pilot with just the two nose machine guns.
It was powered by a single Daimler-Benz DB 605DB/DC engine which had an adjusting screw allowing the engine to use either methanol water injection equipment or C3 fuel.
It began to be delivered in mid-October 1944 and 534 examples were delivered by Messerschmitt AG in Regensburg by the end of November and 856 by the end of the year. By the end of March 1945 Regensburg delivered a total of 1593. However, as war progressed, it became harder to deliver them to the frontlines and it's believed that only 314 K-4s made it successfully to the frontlines, even if it was intended to replace every Bf.109 in service with the K-4, just before jumping into the jet age.
It's not a very known fact but the Italian Social Republic was the only foreign country to receive the K-4. The Aeronautica Nazionale Repubblicana received three K-4s which destined them to the I Gruppo from 28th February 1945 onwards. However, considering the status of the ANR, most probably, they weren't employed in combat.

Sources:
1. https://en.wikipedia.org/wiki/Messerschmitt_Bf_109_variants#Bf_109K
2. Salamander Books - The Complete Book of fighters