What limited wartime shipyard expansion?

How much could the major powers expand shipbuilding if funding was available?

Emergency expansion could be very large, but useful output depended on each country's starting capacity and its ability to supply trained labour without weakening other war needs.

A rough illustration suggests that major powers might double construction capacity under emergency conditions, though the starting base differed greatly by country. New berths and shifts did not automatically create skilled shipbuilders. Expansion pulled experienced people away from existing work or from military service and required new workers to be trained. Britain and the United States benefited from larger pools of retired or semi-retired specialists, women entering war industries, and people medically unavailable for military service. Even a national doubling would be distributed unevenly because some yards had much greater physical room and labour potential than others. The exchange turns shipbuilding capacity from a simple yard-counting exercise into a problem of labour, training, geography, and national mobilisation.