Colonel Bowe was a human who in 1982 hid inside a British nuclear bunker because he thought that there was a nuclear war. However, this was just an illusion created by giant cockroaches, who wanted the humans to stay in the bunker, so that they could use them as a food supply.
When the Eleventh Doctor, Amy Pond and Rory Williams arrived, Bowe thought that they had killed Sergeant Trott. Later he told the Doctor that it didn't matter if they were guilty or not, he would shoot them anyway. Since the nuclear war seemed to be outside they couldn't open the bunker and they didn't have enough food for Amy, Rory and the Doctor.