Effects of Crew promotions and awards

[fidget]

Perhaps somebody has some more insight into this, but I noticed something during my latest 'career'. I'm on the third patrol of my career and was recently given a brand new Gato. After the previous successful patrols, I noticed I could give crew members promotions and awards and did this just as a lark (in the crew management screen). I sprinkled the promotions around more or less randomly (and noticed I could only promote certain crew members). After that, I noticed a definite increase in performance of the boat. I could remain submerged for much longer periods of time than I previously could. The boat could crash dive significantly faster and torpedo reload times were significantly improved. Now, this wasn't very precise comparison and I can't be sure that the promotions did it (i.e., I could have been some kind of experience points awarded to the captain), but I had earlier careers that involved the a Gato where I just ignored promotions and the boat performance seemed to never change with respect to dive time, underwater duration, etc. Anybody else notice this or have insights into the effects of promotions and awards. It would make sense to me if it worked this way and the manual does mention efficiency bonuses based on the officer of the deck's experience but it doesn't go into any more detail than that.