sentences:  It added oak leaf clusters to this award for an attack on oil refineries and marshalling yards at Ploesti, Romania on 5 April 1944 and on Markersdorf-Haindorf Airfield near Vienna, Austria on 23 August 1944.On each of these missions the 451st was opposed by large numbers of enemy interceptor aircraft and heavy flak, but fought its way through to inflict serious damage on the targets and destroy many enemy aircraft.When returning from the Regensburg attack, runway conditions at Gioia del Colle were so poor that the aircraft of the 451st Group were unable to land there, but spread out among a number of bases in Italy.