Gun variants in an enormous Type 45 production run

If Britain built 178 Type 45 destroyers, would some replace the 4.5-inch gun with a 155 mm weapon?

Possibly. A run that large would almost certainly contain variants, and some could carry the larger gun.

The proposed fleet of 178 Type 45 destroyers belongs to the audience's counterfactual rather than any historical program. At that scale, the Royal Navy would almost certainly build several variants instead of keeping one design unchanged. A 155 mm gun is treated as a plausible fit for some ships, although the brief exchange does not define the variant's mission or other changes. The weapon fit remains a possibility within the scenario rather than a prediction.