Sōryū-Class Sub (II)

choi

"The sub also has a secret X configuration rudder design that gives it extra stability[.]"

Mote:
(a) A major selling point in ja.wikipedia.org for "Sōryū-Class Submarines" is X-rudder X舵, compared to cross-shaped rudder 十字型舵, allows a submarine to rest on sea bed -- or when it loses power and sinks, the bottom blade will not get damaged.  However, this is a red herring: in modern submarines, the bottom blade is shorter.
(b) What X-rudder looks like.
(i) arkmodel u31-212a X-rudder system. YouTube.com, uploaded on Jan 31, 2010.
https://www.youtube.com/watch?v=Kbs_q7xnhDc

Arkmodel 方舟模型 is a Chinese toymaker based in Hangzhou.
(ii) Type 212 submarine (German: U212, where U stands for (German noun neuter) Unterseeboot submarine; In commission 2005- ; diesel-electric; AIP)
(c) World's first submarine with X rudder is USS Albacore (AGSS-569)
https://en.wikipedia.org/wiki/USS_Albacore_(AGSS-569)
(a unique [read: experimental] research submarine that pioneered the American version of the teardrop hull form; In commission: 1953-1972; nuclear powered; She was the third ship of the United States Navy to be named for the albacore, a small tuna found in temperate seas throughout the world)

The albacore tuna has 55 to 80 cm fork length. Fork length is one way to measure fish with forked tails: from tip of the snout of closed mouth to the center of the fork in the tail.

US abandoned x-rudder; has not used it again, for whatever reason.
(d) Walrus-class submarine
https://en.wikipedia.org/wiki/Walrus-class_submarine
(section 1 Design)
(e) Rico Jarschke and Roman Schwab, Dive-by-Wire Control on U212A-class Submarines. Undersea Warfare (The official magazine of the US submarine force), Summer 2013, pp 24-25 (Submarine Technology).
www.public.navy.mil/subfor/under ... USW_Summer_2013.pdf
("The X-rudder itself consists of four independently driven blades, each with an angle range of ±35°. Each blade’s angle will have an effect on the course and balance of the submarine. With all four blades, a total angle of ±35° stern plane or rudder can be achieved. * * * Although the maximum angle of any of the X-rudder blades is limited to ±17.5° the boat’s maneuverability is still impressive, even if two blades fail. Thus, the maneuverability is highly redundant, not only through the number of the blades but also by the design of the hydraulic system")