This study gathered evidence concerning the potential usefulness of out-of-the-window air traffic control tower simulation for training tower controllers. Data were collected from all ten developmental controllers who completed simulation training at Chicago O'Hare International Airport during 1994. The simulation included one controller position, outbound ground control. An out-of-the-window view was projected on three visual displays which approximated the size of actual tower windows. Aircraft were representative of O'Hare, and appeared to move in three dimensions on the displays. The simulation could display the entire airport, but only 135 degrees could be seen at a time and no inbound aircraft were simulated. After five weeks of simulation training, the trainees became certified on outbound ground control in 25% fewer days than trainees who received the same amount of traditional training. However, the trainees using the simulation needed only slightly (5%) fewer total hours to become certified on this tower position. Evidence suggested that the simulation increased the trainees' working speed, enabling them to work under busier conditions, and hence more hours per day. Expert ratings of eight ground control skills based on actual tower observations were all higher following simulation training than following traditional training.