Give a Tambor boat a try, if you would, and see if it does the same thing...
Edit; btw, I get the same thing. The Gar is a Tambor boat, but without the HORs engines that breakdown all of the time... The Gar boat that the game gives is the "Gar" itself, first in the series... We'll figure it out... or I should say: "CapnScurvy shall be called upon, and he will probably figure it out"... it could well be something in the CareerStart or Flotillas files that doesn't activate that boat correctly... It is the newest Class of sub at the beginning of the game...