"mystery ship" - a spy ship
"73 men sailed from San Francisco Bay - the Pueble was refit in Bremerton
Washington and then stopped in San Francisco before going overseas to her new
home in Yokosuka Japan. On her first mission she was captured. The crew number
varied but 73 would have been close.
"out on the peaceful sea". The Sea of Japan and/or the straights between Korea
and Japan are translated in either Japanese or Korean as "peaceful sea"