The Tsurugi class of large Aerolyth ships was the first large flying ships developed in Japan after the Otsu incident. As such, their existence was a closely guarded secret to avoid Russian notice. The Imperial Navy officially classifies them as cruisers, but many consider them large enough to be battleships. The Kingdom of Siam’s Khet class is a derivative of the Japanese Tsurugi class. These ships were ordered shortly after the end of the Franco-Siamese War (1893) when Siam began building up its aerial defenses amidst concerns about future European colonization attempts.