Lieutenant Dan Galloway was the weapons officer of the Marine Space Corps expedition to Exxilon. He assumed command of the force after the death of the previous two commanders, as was his duty by rank. However, Commander Stewart ordered him to allow Peter Hamilton to take command, as Stewart didn't feel Galloway had the requisite temperament. Galloway disobeyed, allowing no-one to know the nature of Stewart's final order.
Stewart's concerns were legitimate. Galloway's brief command was characterised by ruthless logic. He made unsavoury deals with the Daleks, promising to commit his forces to a kind of genocide in exchange for their assistance in getting Exxilon's parrinium to the millions of space plague victims off-world. He showed a disdain for the native Exxilons that bordered on xenophobia. Galloway called the Exxilons too "primitive" to worry about. When the Daleks broke the deal, Galloway turned on them. Still committed to his mission, he stowed away on the Dalek ship, and manually detonated a bomb, destroying the ship. In so doing, he sacrificed his own life, and cleared the way for further Marine Space Corps missions to Exxilon. (TV: Death to the Daleks)