I backed up my saves and edited the date month by month until the Snorkel became available. The GWX manual seemed to indicate somewhere around May-August of 1943, but the game actually doesn't let one have it until January 1944. This "jives" with the uboat.net and Wikipedia entries on the subject, though the U-58 is mentioned as having tested one during the summer of 1943.
Hopefully this info will be of use to someone, and they won't be expecting the upgrade in mid 1943 as the GWX manual suggests.
|