Well, I do play it as if I were an actual u-boat commander. The experience of the game is more important to me than sinking everything in sight like I'm using a BFG in Doom II.
If I wanted to rack up massive, arcade style tonnage I'd go play Sub-Roc on my old Sega Genesis. :p
I stay out as long as fuel and provisions allow. The only time I've ever returned to port with eels still in my belly was the time my bow tubes got destroyed from depth charges. I rarely use the deck gun these days because most of the merchants are now armed and travel in convoys as I'm approaching mid-1941. Lone merchants are usually close enough to land that air cover makes a surface attack nearly suicidal.
That said, my own best patrol was when I ran across a task force and sank a Revenge-class BB then later savaged a large convoy for a total of 64,601 tonnes. That BB made up for about half of that!
Let's raise a toast to StarLion45, especially since he's buying!
Here's to sinking 100,000 more, kaleun!