By request of German authorities, automotive player Daimler-Gesellschaft-Werke (Daimler) established an aircraft-making division in middle of 1915 as World War 1 (1914-1918) raged on across Europe. From this was drawn up plans for an in-house single-seat, single-engine fighter biplane to rely on the equally in-house Daimler D.IIIb series 8V water-cooled engine of 185 horsepower. The aircraft became the "L6" and was type certified by German authorities in a 1918 fighter competition - an order for twenty was ultimately had (to carry the "D.I" designation). However, the end of the war meant that only six of the type would ever be completed.
Beyond this, the company went to work during the wartime years on yet another design - this time a twin-seat, single-engine biplane intended for the escort fighter role. The wing structure utilized an unequal span, single bay approach and one machine gun was afforded to the pilot while an observer/rear gunner managed another weapon on a trainable mounting facing mainly to the rear. The aircraft, the "L8", was dimensionally larger in all directions but slower as performance compared to the earlier L6 - though with greatly enhanced range (four hours versus two) and a more flexible weapons loadout. In any event, the design fell to naught as just a single, flyable prototype was realized before the Armistice of November 1918. An offer to Chile for this aircraft also fell through in July 1919. It was to carry the "Cl.I" designation in German service.
Continuing with the promising L6 design, Daimler engineers reworked the fighter to become the "L9" ("D.II"). By all accounts, the L9 was a further evolution of the line begun in 1917, eventually deleting the original parallel struts of the mainplanes and adding single "I-type" supports in their place. The equal-span wings were also modified into unequal planes with the larger member being of greater span than the lower. The fighter retained the streamlined forms of the L6 and L8 before it and carried an oversized spinner at the two-bladed wooden propeller for enhanced aerodynamic efficiency. Beyond this, the fighter was given the same Daimler D.IIIb V8 water-cooled engine of 185 horsepower as the others before it and had a twin 7.92mm LMG 08/15 machine gun arrangement over the nose similar to the L6 - these weapons synchronized to fire through the spinning propeller blades. Ground-running was through a conventional / traditional tail-dragger configuration.
The original aircraft was worked on into July 1918 and its new I-type struts were added in August of that year. However, like other Daimler-originated fighters of the period, the design was ended with the end of the war in November of 1918 with just a single prototype completed. In 1920, Daimler attempted to interest global carriers in the idea of the L9 as a mailplane but this modification initiative went nowhere.
For its short time in the air, the L9/D.II recorded a maximum speed of 118 miles-per-hour with a range out to 275 miles, and a rate-of-climb near 905 feet-per-minute (initial rate). Empty weight was 1,635lb against a Maximum Take-Off Weight (MTOW) of 2,185lb. Dimensions included a running length of 23.7 feet, a wingspan of 29.6 feet, and a height of 8.6 feet.