 During the 1930s, both ships underwent a series of modernizations and reconstructions. Fusō underwent her modernization in two phases (1930 – 33, 1937 – 41), while Yamashiro was reconstructed from 1930 to 1935. The modernization increased their armor, replaced and upgraded their machinery, and rebuilt their superstructures into the distinctive pagoda mast style. Despite the expensive reconstructions, both vessels were considered obsolescent by the eve of World War II, and neither saw significant action in the early years of the war. Fusō served as a troop transport in 1943, while Yamashiro was relegated to training duty in the Inland Sea. Both underwent upgrades to their anti-aircraft suite in 1944 before transferring to Singapore in August 1944.
