The Sub-Commander was a rank given to certain members of the Ice Warriors' society. Sstast who served as second-in-command to Ice Lord Commander Zzaal held the rank of sub-commander. (AUDIO: Red Dawn)
The Dalek Survival Guide noted the Gold Dalek as a Dalek Supreme yet also claimed the Dalek was never called by that rank, leading to the theory that it was actually a sub-commander or Chief. (PROSE: Dalek Survival Guide)