The choice between gun caliber and speed was political as well as technical

The Royal Navy already depended on thirteen major ships armed with 15-inch guns and needed fast capital ships able to move around a global empire. A new 15-inch/50 weapon could support fleet standardization while freeing weight for machinery. In this interpretation, Nelson's slow, heavily protected design reflected political attraction to an apparently unsinkable centerpiece of the battle line. Political choices provide the counterfactual's starting point because they involve judgments that could have gone another way. Britain could have presented a smaller-caliber design as a gesture of confidence in naval arms limitation while gaining useful speed. The scenario is most persuasive through design, construction, and the first London treaty, since later events introduce too many interacting changes.