Tosa is more useful to Japan in this setup than one isolated battlecruiser alongside the four Kongos. Completing the 39,000-ton battleship improves Japan's special-ship position and gives its negotiators a visible success. Britain and the United States could also prefer allowing one Japanese battleship to reopening the argument over two additional battlecruisers. The concession may leave Japan more satisfied with this settlement than it was with the historical Washington agreement.
Chapter · 26:53-30:20
Tosa gives Japan a visible treaty win
Japan's incentive in the altered settlement is completing Tosa, gaining a prestige battleship without making the treaty collapse.