Treaty tonnage rewards submarine numbers over maximum size

How would a treaty allowing 4,000-ton submarines and large aggregate tonnage shape fleet design?

Navies would still favor enough smaller boats to meet deployment needs, using auxiliary tenders outside the limit and only selectively building larger specialist submarines.

A 4,000-ton standard-displacement submarine approaches the scale of Japan's I-400 class. Spending a 100,000-ton allowance entirely on such boats yields only twenty-five submarines when major navies seek roughly sixty to ninety. Submarine tenders would be built as auxiliaries outside the combat tonnage limit, while mine-laying designs might grow modestly for fuel, batteries, and additional mines without approaching the maximum.