The Lysander was an early "STOL" aircraft and entered active service during WWII. Initial design work began in 1935 in response to an official Air Ministry specification to replace the obsolete Audax in service with the RAF. The design embodied many refinements developed high lift properties of various wing incorporating leading edge slats, and special trailing edge flaps which provided positive control in flight at very low ground speeds. In Germany, the Fiesler Storch was developed for the same purpose.