The Fortresses were used for very high-altitude attacks in daylight, the first operation from Polebrook being flown on 8 July 1941 when three Fortresses were dispatched on a raid to Wilhelmshaven. Engine trouble forced one of the planes to divert to a second target, but the other two went on to attack the naval barracks at Wilhelmshaven from an altitude of 30,000 feet. Unfortunately, the planes were not able to hit anything from such extreme altitudes. In addition, their crews found that the temperatures at this altitude were so cold that their defensive machine guns froze up when they tried to fire them. However, all planes returned safely to base.