Career vs. number of patrols

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Hello,
I was wondering if, historically speaking, a Uboat commander started his career in '39 and ended with the wars end, what would be the average number of patrols he would have completed? If this was indeed possible? Or did that even exist?
I'm on my first career, late 42, and I'm up to 28 patrols.
just curious.

I have my time spent in base at 28 days.

I am not playing dead is dead, this being my first career and I want to see what all goodies you can get later in the war. But my next career will probably be a higher realism level, except I dont think I can do without external cam, and played at dead is dead level.
thanks

EDIT: I just thought of this... how do you find dolphins? I've seen pictures here, but have never seen one in the game.