Mark Douglas 
There and Back Again in North Korea [EPUB ebook] 

In the continuing series, the Hoquiam returns to there North Korean East coast running back and forth between Wonsan and Sosura. Targets include roads, bridges, trains, and other targets of opportunity. She is allowed to return to Sasebo and Yokosuka, Japan for short periods of rest and ship upkeep. Their favorite targets are the narrow-gauge trains that run between Manchuria and various North Korean and Chinese bases. Usually, they catch them between tunnels.