The designation Ikarus 451 covers a family of six research aircraft designs built in Yugoslavia in the 1950s, all sharing the same basic airframe, but otherwise quite different from each other. One member of the family Ikarus 451M became the first domestically-built jet aircraft to fly in Yugoslavia, on 25 October 1952.
The first aircraft built under this designation was a propeller-driven aircraft that accommodated the pilot in prone position. It was an otherwise conventional low-wing monoplane with retractable tailwheel undercarriage, the main units of which retracted backwards into the engine nacelles mounted below the wings. This flew in 1952, and by the end of the year was followed by the 451M (Mlazni - "Jet") which had conventional seating for the pilot and in place of the two Walter Minor 6-III inline engines of the original Ikarus 451 (which has two inverted Walter six-cylinder piston engines of 118 kW (158 bhp) each, 6.7m (22 ft) wingspan, a maximum speed of 335 km/h (182 knots) and a ceiling of 4750m (15,570 ft).) was fitted with Turboméca Palas turbojets. In this version, the undercarriage retracted inwards. Provision was made to carry one 20 mm Hispano Suiza 404A cannon under the fuselage, plus six RS rockets under the wings. Further developments were aimed at developing a viable military aircraft from this basic design.