The missing escorts in Japan's Circle One programme

Was Japan's pre-war Circle One programme too little and too late?

Its major weakness was inadequate investment in minesweepers and submarine chasers, ships Japan could have built in larger numbers outside treaty constraints.

The programme appears too restrained in escort and anti-submarine capacity, particularly once Japan expected later expansion and wider operations. Minesweepers and submarine chasers were not constrained by the same treaty limits as capital ships, so they offered a practical place to build numbers. Building a few experimental chasers was sensible, but Japan needed to test them and then copy them at scale. The weakness lay in failing to turn trial designs into the mass of unglamorous ships a major war would require.