The Tomozuru Incident of 12 March 1934, in which a top-heavy torpedo boat capsized in heavy weather, caused the IJN to investigate the stability of all their ships, resulting in design changes to improve stability and increase hull strength. "Ryūjō", already known to be only marginally stable, was promptly docked at the Kure Naval Arsenal for modifications that strengthened her keel and added ballast and shallow torpedo bulges to improve her stability. Her funnels were moved higher up the side of her hull and curved downward to keep the deck clear of smoke.