The best strategy i have used is to submerge through most of the biscay crossing... the shallow waters preclude crash dives.
secondly, when your in deeper waters stay submerged to about 40 meters just long enough to use up about 25% of your battery... only surfacing to recharge that 25%.
get the snorkel as soon as you can and stay submerged using the snorkel in short 10 minute bursts to recharge. The allies knew that the U-boats covered a lot of ground on the surface and that by using airplanes to keep them submerged the range and attack capability of the U-boats was greatly impacted. any look at U-bot fates in U-boats.net will reveal that most U-boats were victims of air attacks.
U-Flak is good too but only if you are faced with something like a swordfish bomber. on the other hand if you try and use the U-flak against a couple of mosquitoes you will be woefully dissapointed in how quickly your U-boat sinks after a rocket attack.
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