My last two patrols, AM53 and BF14, were just like that...miserable weather with visibility less than 1000 meters during the day and around 600 meters at night. The seas were heaving so badly that my watch crew spent a good portion of their time underwater from the swells swamping our u-boat.
The periscope was nearly useless and the bow was pitching up and down so much that it was nearly impossible to launch a torpedo with any great accuracy.
In situations like that, all you can do is set you eels for a surface run ( 0 depth ), and hope a swell doesn't lift your target's hull above the path of your torpedo.
Bagged only an average 9,000 tons on each of those patrols.
Nothing more frustrating and disheartening that a winter patrol in the North Atlantic.
