I'm going to add modified
SpecialAbilities.upc file to the archive in order to prevent some unrealistic and historically unconfirmed features, like crazy submarine speed well above 20 knots with engine overcharge ability or navigator who can "somehow" increase maximum depth of the submarine...
This changes are necessary in order to sustain U-Boat performance as close as possible to the real thing but this will also require fresh campaign start so hold your horses until then...
EDIT:
Done...Now, because of the modified points requirements for certain abilities, some upgrades will be blocked while others will be "free" from the beginning (like max dive ability).