Pearl to Japan, stop at Midway along the way and top off your fuel tanks. There are no bases closer until into 1944. It is usually best to stay on the surface as much as possible. If you have air search radar, use it, and dive if necessary. Follow the Rockin Robbins' Rule:
When you dive and use batteries, the batteries get charged when you surface, which reduces your fuel efficiency, since one of the engines charges, while the other propels the boat. You can do what Captain_AJ suggests to preserve battery and fuel, but not letting the battery get down to begin with is better.
For most mods and Stock, for best fuel efficiency, use no more than Ahead Standard. A couple of them have Ahead Two Thirds (Slow), and another will have you set the speed on the knots dial Hover your mouse over that "boxy" area below the speed telegraph dial, and you'll get this (no red arrow, of course):
Click that area, and you get the knots. Click it again, and you're back to the telegraph
Likewise with the direction via compass to degrees of turn and back:
... and the depth gauge shallow and deep:
... and, of course, stop at Midway on the way back and get more fuel...
