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What does "Zuiun" mean?
Short answer
"Zuiun" means "auspicious cloud": that was the name given to the Navy's Zuiun Reconnaissance Floatplane Model 11. The aircraft, the Aichi E16A, was conceived as a replacement for the Aichi E13A, and work began in 1940 under the designation AM-22. The first prototype was completed in May 1942.

"Auspicious cloud"
The aircraft's official designation was the Navy Zuiun ("auspicious cloud") Reconnaissance Floatplane Model 11.
From AM-22 to "Number 16" specification
Conceived as a replacement for the Aichi E13A, the design work began under the designation AM-22 in 1940. In January 1941 Japanese naval aviation drew up a new "Number 16" specification around Aichi's AM-22 design. The first prototype was completed in May 1942. Aichi's Eitoku plant delivered 197 units, and Nippon Hikōki a further 59.
Philippines and Okinawa
The type entered service with Japanese naval aviation in early 1944, by which time the Allies had already gained air superiority. It suffered a high attrition rate throughout its operational life, especially during the Philippines campaign. The E16A1 Zuiun was used heavily against the US invasion of the Philippines in 1944, with heavy losses. After that campaign, most of the remaining E16As were expended in kamikaze attacks near Okinawa.
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