On June 13, 1943, three B-17 bombers of the 393rd Bomb Group, the Flying Sioux, left the Sioux City, Iowa, airbase on a routine training mission. After three hours of rigorous flying, flights 750 and 790 collided while maneuvering to switch formation at 3,000 feet, and 790's propellers cut off the tail section of 750. Lt. O.B. Groves instantly lost control of the tailless plane, and the crew of plane 446, piloted by Lt. Fred Glazier, watched as it did a half loop and crashed on its back, killing ten airmen aboard at once; the tail gunner, thrown from the severed tail section, was also killed. Plane 790, with two engines out and a third on fire, was so badly damaged that it struggled on for another eight miles before belly landing on a creek bank, but through Lt. Billy Fuller's skill all aboard survived. After witnessing the accident, plane 446 radioed in and returned to base in Sioux City. Those killed in plane 750 were Lt. O.B. Groves, 2nd Lt. Michael R. Hric, 2nd Lt. Roy B. Lever, 2nd Lt. James J. O'Connell, S/Sgt. Rodney T. Cassidy, Sgt. Sidney S. Packer, S/Sgt. Dean M. Garland, S/Sgt. Murry V. Whitehead, Marvin J. Curtis, S/Sgt. Charles R. Bowers, and S/Sgt. Bruno E. Twardy. The crash site of plane 750 lies about two and one-half miles southeast in Clinton Township in Miner County, South Dakota, and the site where plane 790 crash-landed lies eight miles farther south-southeast in Rock Creek Township. The disaster was the single biggest air disaster in the history of Miner County or South Dakota.