Developed in 1955, the AT-21 was of conventional aircraft design, with a high-mounted, constant-
chord monoplane wing and a
twin tail empennage. Power was provided by a
SNECMA AS-11 Ecrevisse pulsejet, mounted in a
fairing underneath the aircraft's
fuselage; the construction of the airframe made extensive use of
plastic in the nose and tail, with the center-section being of metal construction, and the wings and tail were made of foam-filled plastic with metal
stabilizers and
rudders. ==Operational history==