Unknown (most likely dead)
Mars City Underground (PDA audio log only)
Frank A. Delahue is a background character in Doom 3. He was the Engineering Manager for the Mars City Underground, and was responsible for overseeing power production for Mars City. In the month prior to the events of Doom 3, he voiced his concerns with the constant energy demands from the Delta Complex (due to their secret teleportation experiments) which were straining the base's power grid. Delahue worried that they wouldn't be able to maintain these power levels for long, and that key systems would be shut down as a result. He stated in his PDA report that if things didn't get better soon, "all hell was going to break loose."
Delahue's PDA can be found on a control console in the Energy Processing room in the Mars City Underground. It is needed to access a security door. The PDA also contains the failure code 842 which enables the player to extinguish a fire and gain access to some supplies.
Delahue was also friends with Delta Labs engineer Brian Mora, as Brian invited him to a party in Delta.
Delahue himself is never encountered in the game. He was presumably killed or turned into a zombie during the demonic invasion.