"As far as I know they were only ever employed on convoys to Russia."
Not so Schiller.
There was a gap in the Allies air cover in the mid Atlantic.
The Condor had the range to cover that area and report the position of convoys for their U-boats.
CAM ships were introduced to deny the Condors the free range they had previously enjoyed in that mid Atlantic gap.
That is where most of them were used.