According to Steven Moffat, Captain Jack Harkness was going to be part of The Doctor's Army. However, John Barrowman was filming Season Four of Torchwood (2006) ("Miracle Day") in America. Moffat said that it was just as well, since he would have had to make the episode about not only Jack returning, but getting used to the Eleventh Doctor.
This is the first story to include River where the phrase "Hello Sweetie" isn't heard.
Paul Kasey's appearance as Ood Sigma was edited out. He was to fight for the Doctor by singing a melody which forced the Headless Monks into prayer. Despite the cut, Russell T. Davies would nonetheless receive a credit as the Ood's creator.
The various sets seen at the beginning of the episode were challenging for the production team.
The episode's idea stemmed from Steven Moffat wondering if the Doctor, who was typically a pacifist, could be provoked enough to assemble an army.