"On the basis of his previous project, type 451, engineer Dragoljub Bešlin, heading the Designers Group No. 9, of the General Direction of Aeronautical Industry, created the first Yugoslav jet plane, type 451 M, letter M meaning "mlazni” – jet, keeping, in general, the shape and dimensions of the 451 type. Instead of piston engines turbojets were built in, and cockpit was conventional, pilot in seating position. The prototype was built by "Ikarus” aircraft factory, and the first test flight performed test pilot Tugomir Prebeg on 25th October 1952. opening Yugoslav jet aviation era half a year before the first American jet planes T-33A arrived. The only one 451M prototype was made, and flew until 1959, when was removed from an inventory and handed over to the Air Museum.
Soon appeared a variant of this plane, unarmed S 451M Zolja, (Wasp), differing of 451M in engine placement (in wings axis), built also in one sample. After completing trails, done at the Air Test Center, plane got civil registration YU-COH, and on 19th May 1960, pilot Ivan Črnjarić, as member of Aeroclub "Franjo Kluz”, Zemun, piloting "Zolja”, beat the world speed record in I-C aircraft category, flying 501 kmph, result unbeaten next five years. "Zolja” was removed from an inventory 1968 due to damage in incident on the apron.
In general, designing and building in Yugoslavia a "family” of experimental aircraft, propelled by jet engines of modest power, built mainly as a prototypes, or sometimes a few more samples, aimed to examine planes’ different aerodynamically, technical, technological and other practical solutions. By their appearance, Yugoslavia became the first country in region designing and producing own jet planes."
