John, the "jaunt up to Murmansk" I think goes a bit deeper than that. The pool system of crewing ships was used during the war and Murmansk was the destination of the artic convoys to supply Russia. The PQ convoys were and are generally acknowledged to be the most dangerous regular convoy run of the war. "Fourth" would have been fourth mate. "Pusser" is the Navy term for purser, and was in common use as a descriptive for the Andrew by men of the merchant marine. Just in case its not obvious to anyone, the Red duster is the Red Ensign worn by British Merchantmen.
Just as an aside it is not generally appreciated that the most dangerous service in the second world war in terms of percentage of men killed and wounded was the Merchant Marine.