As a result of the London naval treaty, one-fourth of a country's cruisers could be equipped with attack aircraft. The U.S. built the Tiburon-class for wheeled craft, and the Japanese built the Sagamis for fast seaplanes. Tiburon sacrificed gunpower, but Sagami did not. By grouping the main armament forward it would have all the normal gunpower of a heavy cruiser plus scouting and attack aircraft. It wasn't meant to tackle 'real' aircraft carriers, but rather any scouting ships that had no such aircraft.

Sagami was sunk and nearly destroyed in an accidental exlosion in port. She was raised, rebuilt, and became Goryo. Sister ship Chikuma was sunk and Tone suffered badly off Samar in the Fall of 1941 as British and Dutch aircraft tore apart a fast battle squadron that both ships were escorting. Tone was repaired in Japan, and it was her scout aircraft which gave Tokyo warning of Doolittle's raiders on their way . Tone's Seiran floatplanes were used as interceptors in a big fleet confrontation in the Indian Ocean. Planes from the Dutch CV Molucca sank Tone despite this aircover. The Japanese wanted full-fledged carriers from then on, so no more 'flight-deck cruisers' were made.