The "Walrus"-class submarines are unusual in that instead of a cross-shaped assembly of stern diving planes and rudders, they mount four combined rudders and diving planes in an "X" configuration. This tail configuration was first tested in 1960 on the United States Navy's , and has since been used by the "Walrus" class, all Swedish Navy submarines since the , the Royal Australian Navy's , the German Navy Type 212A and the Japan Maritime Self-Defense Force's . The X configuration is a complex system and therefore not implemented by many other navies around the world.