This is a very minor curiousity. The Royal Navy's C class cruisers comprised 28 ships of seven progressively improved designs, 13 of which were still serving in WWII. The last two variants - Ceres and Carlisle classes - were the most advanced. Their most notable feature was the redesign of the forward superstructure to accommodate a second, superfiring, B gun position with a clear arc of fire across the bow. Earlier ships including the three surviving Caledons had the second gun aft of the bridge and foremast, with only a limited arc of fire to each side. In the late 1930s six of the Ceres/Cardiff classes were converted to AA cruisers. When war came, they were in the thick of the action, all six were eventually lost, but they shot down almost 1/3 of all aircraft destroyed by RN cruisers (Carlisle, the last survior, had the highest individual score, 11). In 1942-43 two more were converted to AA ships, Colombo of the Carlisle class and - here's what I find strange - Caledon. Caledon had to have her forward superstructure rebuilt to incorporate a B position, which seems like a lot of extra work given that three more ships with the B gun arrangement - Cardiff, Ceres, and Capetown - were available. Capetown had been torpedoed by an MAS boat in 1941 but was repaired and was still operational for Neptune/Overlord in June 1944, as was Ceres. Small point but it seems like unnecessary extra work.
The other 3 may have been seen as good enough at the time where Caledon may have been viewed as needing an overhaul to reach some minimum of efficiency. Once in the yards the work on the superstruture may have been able to be executed simultaneously or at least without in significant extra time in the yard. It would very much depend on what the constraints were. If it were yard space then it makes a great deal of sense. If labor was a serious constraint perhpaps not.
The short answer is that the intent was for Colombo and Capetown to be converted in 1942. They had already been selected for conversion to AA cruisers, their turns would’ve come in mid/late 1939, but the war intervened, plans were put on hold, they went off to serve as 2[SUP]nd [/SUP]tier 6” cruisers. When yard space became available in 1942, Capetown was still in a drydock in India, having the torpedo damage she received in the Red Sea repaired. It took forever, largely because war had intervened again, even the Fleet had moved to the other side of the Indian Ocean. Colombo was sent back from Eastern waters, then Caledon, to fill the spot that would’ve been Capetown’s. There’s a great deal of background as well. Briefly going back to 1936 and Treaty considerations whereby only 6 of the C’s would be retained, 5 converting to AA cruisers, and that they’d be scrapped by 1941. Months later i.e. early 1937 the intent was to convert the VW Destroyers and Sloops to AA convoy escorts., as well as 6 C’s, 8 D’s (with twin 4.5” turrets), and certain merchant cruisers with the same AA conversion as the C’s. The 1[SUP]st[/SUP] 5 C’s selected in 1937 for conversion in 1938 included Caledon, Caradoc and Calypso of the older sub-class (armament for the 6[SUP]th[/SUP], was to go to HMS Whitley, a VW Destroyer) . Then six more would be converted in 1939, but shortly thereafter, Caledon, Caradoc and Calypso were omitted from the 1938 and 1939 lists, because of the additional expense involved in moving the superstructure back, adding a shelter deck for a superfiring turret, and the internal changes required. Consideration was also given to converting more VW’s, Sloops etc., at the expense of C’s, intended for scrapping in 1941, so the lists were provisional. In any case, Fleet vessels, and more modern escorts took priority when it came to AA upgrade – everything was pushed back some, resulting in only 4 more conversions (after the original pair, Coventry & Curlew) before the war. Of the remaining C’s, Cardiff had already been converted into a gunnery training ship, Ceres was retained in the East, Caradoc was sent East as a replacement for Caledon & Colombo. I suspect that mid-1942, given how the war had developed, there was serious intent to convert Ceres, Capetown and perhaps Caradoc as well, time permitting. In the rosier glow of 1943 it was determined that any conversion in scale on these ships was a waste, so it didn't happen.
