Apart from the fact that it is boring, time consuming, difficult and irritating, there are two ways that I regularly use to get at least a reasonable number of kills during those fortnight long storms that apparently we Englishers live with. Both depend on being submerged somwhere with plenty of contacts, e.g. any of the approaches to Great Britain, neither depend on radar or active sonar so can be used early war. Surface only to recharge batteries.
The first is a somewhat unhistorical but very effective target motion analysis described here:
http://www.subsim.com/radioroom/showthread.php?t=110619
the second is the method i described in the article in my sig link which is similar to late war us submarine doctrine and utilises the SACF, or Is-was. You have built yourself an Is-was, haven't you?