Koolhoven's first design for Armstrong Whitworth was a small, single-seat, aircraft intended as a scout aircraft. A single-bay tractorbiplane, the Sissit, or F.K.1 was fitted with balanced elevators and no fixed tailplane.
Although designed for an 80 hp (60 kW) Gnômerotary engine, only a 50 hp (37 kW) Gnôme could be obtained. Fitted with this engine, it was first flown by Koolhaven in September 1914. It proved to be underpowered, and was modified with a fixed tailplane and enlarged ailerons. As greatly superior single seat scout aircraft such as the Sopwith Tabloid and Bristol Scout were already available, no further development of the Sissit took place.