By 1934, the autogyro form of aircraft, developed by Señor Juan de la Cierva, a Spaniard, was sufficiently advanced for the Royal Air Force to order a small number of C-30As for evaluation on army co-operation duties. However, by the outbreak of World War Two they had been allocated for use by a highly secret unit engaged on ground radar calibration duties. The C-30A was the most widely produced Cierva autogyro design. Avro built the type under licence, as the Avro Type 671 Rota, both for the ci