The unconventional twin-boom airplane project under Jaroslav Šlechta began in 1936 as a response to a Ministry of National Defence specification which called for the design and construction of a new reconnaissance aircraft to operate over combat zones. The short-range reconnaissance three-seater was to be capable of monitoring activity behind enemy lines; the requirement highlighted the importance of good view from the cockpit as well as of placement of the on-board cameras, which were to be able to collect as many shots as possible at as wide an angle as possible in one flyover. The new aircraft was to replace the aging Letov Š-328 and Aero A-100. There were three entries to the tender: the Letov Š-50, the ČKD-Praga E-51 and the Aero A-304.
