The "O" class is actually 2 distinct groups of ships. The first 4 were completed as planned with the 4.7" main battery with 2 quad torpedo mounts and a single 4" AA mount. This is represented by the Oribi.
The second group, as represented by the Orwell, was an attempt to strengthen the AA armament for the later "O" class ships. It was proposed to replace the single 4.7" mounts with twin 4" mounts along with the single 4" AA mount. In order to balance the weights, one of the quad torpedo tubes was removed. This conversion, however, was shelved and the single 4.7" mounts were replaced with single 4" mounts. So the armament ended up as 4 4" guns in the usual two turrets fore and aft, a single 4" AA in the torpedo position, and a single quad torpedo mount.
The reason for the one 4" mount in red is to show that this gun is NOT tied into the fire control system for the main battery. In surface combat, the 4 main guns would fire under director control while the single 4" AA would fire under local control.
At this time there are no plans to expand the logs to include the Dominion fleets.