One of the main reasons for the high loss rate amongst Japanese submarines in the Pacific War was their comparatively large radar and sonar cross section, making them easily detectable to American radars and passive and active sonars. Despite Japanese steel metallurgy being somewhat inferior to that of the Western nation, it is claimed that some later submarines were given oblique-surfaced conning towers to reduce their radar cross-sections. Whilst this innovation may not have been very successful at the time, it must be one of the earliest examples of 'Stealth Technology'.
