Seriously, I think the impact of
Resistance as a BC depends on where she falls in the RN leapfrogging around the fleet trying to keep the older ships modern. If she falls with
Barham and
Royal Oak, she'll be limited, as was
Repulse falling with
Malaya. Ideally, she might fall with
Renown, but that might necessitate foregoing
QE or
Valiant. IIRC, Peter C Smith said Sommerville specifically chose
Renown for his flagship over
Repulse due to her AA firepower.
I think it's likely
Resistance might go in the yards with
Warspite, get re-boilered, have her main gun elevation increased and have an all-4in DP secondary; I really can't see the RN keeping the 4in triple LA mounts with 4in HA. (
Warspite historically had 4 x 4in twins fitted for AA and kept some of her 6in casemates.)
As for impact, an additional fast capital ship will be boon to the RN. She would be hunting the
Graf Spee,
Scheer, the twins and
Hipper if she were with the Home Fleet early in the war. She might be assigned to Gibraltar to give Sommerville an additional fast capital ship, which might mean she participates in Catapult, Grog and Spartivento.
If with the Home Fleet in 1941, she would be with the Battlecruiser Squadron, which might mean
Prince of Wales is not rushed to completion.
Resistance and
Hood go to Denmark Strait. Assuming
Hood is still lost,
Resistance will shadow
Bismarck; if her endurance is as good as
Renown, she might be present for the final battle.
If not in need of a refit later in the year, she might get sent east with
Prince of Wales. An additional ship with modern AA would help Phillips, but it probably won't save his command. There is a chance that
Resistance and
Repulse might survive and be withdrawn. They would give Sommerville a fast wing and good carrier escorts for his Eastern Fleet in 1942.
If not sent east,
Resistance will spell
Renown at Gibraltar and spare Sommerville from flying his flag on
Malaya when
Renown gets her refit.
Renown joined the Home Fleet after that refit, so
Resistance will stay in Gibraltar.
Barring an unforeseen appointment with a U-boat or Italian frogmen,
Resistance will be sent to the Indian Ocean in 1944 and stay in the Far East until the end of the war, refits aside. Likely in better shape than
Renown at this point (less stress on the hull from 4in twin deck mounts versus
Renown's 4.5in between-deck turrets) she will be a great carrier escort, as
Renown was. She'll join the British Pacific Fleet when it forms for the final assault on Japan. She might even get in the battleline with
King George V and the US battleships to bombard the Hitachi steel works near Tokyo.
My initial thoughts,