Gail Purdy

Lieutenant Commander Gail Purdy was a member of the UNSC Navy and an engineer in 2552. She was assigned to the as Chief Engineer. She was not in the same Chain of Command as the ODST officers, but she clearly outranked First Lieutenant Melissa McKay. She was middle aged and stout, with ginger-colored hair and stern and serious eyes.

She was aboard the Pillar of Autumn when it arrived at Installation 04. Presumably, she took a Bumblebee life pod to the surface when the vessel crashed. At Alpha Base, she managed to survive until the very end of the event. She was one of the few specialists that was assigned guards during the ODST attack on the Truth and Reconciliation. She pointed out a conduit to McKay that she knew was vital to the function of the ship. McKay ends up destroying that very piece of technology to stop the Flood from getting to Earth.

The naval rank of Lieutenant Commander is at the same pay grade as the Marine rank of Major. Therefore, Major Antonio Silva, the commander of the ODST forces, is actually the same rank as Purdy. However, since she does not specialize in a combat field, he would assume tactical command. Also, it is never directly stated that she is the Chief Engineer of the vessel, but at her high pay grade, it is easy to assume that she is the highest ranking engineer aboard the ship, therefore making her the Chief.