Sergeant Jones was given the overall responsibility for Bombe maintenance by Edward Travis. Later Squadron Leader and not to be confused with Eric Jones, he was one of the original bombe maintenance engineers, and experienced in BTM techniques. Welchman said that later in the war when other people tried to maintain them, they realised how lucky they were to have him. About 15 million delicate wire brushes on the drums had to make reliable contact with the terminals on the template. There were 104 brushes per drum, 720 drums per bombe, and ultimately around 200 bombes.