The first Dornier Do K was the K1 which first flew on 7 May 1929. The K1 was a conventionally-braced high-wing monoplane, powered by a single nose-mounted licence-built Bristol Jupiter VIradial engine, and had a conventional landing gear with a tailskid. The square-section fuselage had an enclosed cockpit for two with a cabin behind for freight or eight passengers. Test flights showed that performance was poor and the aircraft was redesigned.
The K3 was a complete rethink of the design. The braced wing was replaced with a cantilever wing of larger span. The fuselage was changed to oval and stretched for two extra passengers and the tailskid was replaced with a tailwheel and the main units were enclosed in fairings. The four engines were in the same tandem arrangement as the K2, but located lower on the fuselage and changed to Walter Castor radial engines. The performance was greatly improved but still provoked little interest and no others were built.