It's just Attack Squad Delta in the story, isn't it?
Talk about it here.
Dalek Attack Squad Delta was a squadron comprised of three Daleks. This squad was sent on Galacton to investigate the disappearance of two Daleks who failed to return after drilling boreholes to the planet's core. A group of red-eyed creatures attacked and destroyed the squadron save for the Dalek Attack Squad Leader, who energised the planet's core and sacrificed its life to destroy Galacton. (PROSE: Mission to Galacton)