Bücker Bü 131 Jungmann CASA 1.131

The Jungmann reached Spain with the Condor Legion: the first three landed in November 1936 and Germany went on to supply 95 aircraft —more than a hundred according to British and German sources—, initially assigned to the elementary school at El Copero (Seville). The Nationalist side applied for and was granted a production licence for Construcciones Aeronáuticas S.A. (CASA), which set it up at its Cádiz factory. The manufacturer's designation was CASA 1.131 and the military one E.3B, with an individual number assigned to each airframe by the Spanish Air Force.

Sources differ on the starting date: the Air Britain Digest and the German Wikipedia place the first Spanish-built examples in 1938, whereas the Spanish documentation —Spanish Wikipedia and the Fundación Infante de Orleans— dates the maiden flight of "the first Spanish Bücker" to 14 March 1941, after the civil war. All agree on the essentials: the first 200 aircraft carried the German-built Hirth HM 504. The CASA Jungmann Research Team identifies them as licence-built Bü 131-D2s. From the 201st aircraft onwards the Spanish ENMA Tigre engine was fitted, giving rise to the 1.131E and 1.131L versions; and 30 of these Hirth aircraft were later converted to the Tigre, carrying a second manufacturer's plate that still identifies them today.

With 550 new aircraft and 30 rebuilt ones, the CASA 1.131 was the most numerous aircraft in the history of the Spanish Air Force and its primary trainer until 1968; the last examples were struck off in 1988, after half a century of service.