Odd fuel mileage?
 

I left Honshu with 56% fuel left, somehow I didn't manage to make it back to Midway with that much?

Possible bug?

Depends on your speed, weather conditions, how much time you spent charging your battery.... no two trips are the same.

JCC

Not a bug but bad fuel ecomony with speed the devs made. You need to run around 11 kts for good fuel economy. When in you patrol area run around 7 knots to help with fuel.

Damage can cause this as well. I don't think fuel leaks are specifically called out on the damage interface, but they can occur.

JD

If you took any damage, then it's likely that your battery just kept recharging all the time. Depletes your fuel VERY quickly.

Weather is a significant factor even in an undamaged boat. The higher the wind/waves, the more fuel you waste trying to churn at high speed. I always give myself a 10% extra margin on the return trip and use ahead 1/3 when the wind is higher than 10 m/sec. This higher margin will allow for some high speed attacks or evasions requiring long charging times as well as unusual weather on the way back. You can't always count on the weather being the same returning as going out.
-Pv-

I has the same problem, I always run at 1/3 while on patrol and head home when the fuel level is about 50%.. So far it has always worked, but last night I suddenly ran out of fuel about 1/3 the way home. Now I am sitting out in the middle of nowhere with no way to get home. I had hull damage of about 20% but no warning of a fuel leak, which in a real boat the engineer would know right away. I cannot find any indication on the damage screen of a fuel leak. Now that I am stranded, how do I end the mission? Thanks! Joe S

Did you check that the batteries are not charging? In a damaged boat they often charge up to 99%, and then you get the report "Batteries charged 100%". Because they actually are at 99% though, the loading goes on and on... and you run out of fuel because the fuel consumption is phenomenal. Rough weather does not make such a huge difference, that you wouldn't make it home from any of the normal patrol areas with 50% of fuel remaining, provided that you run at the most economical speed(~9 - 10 knots in fleet boats) and on surface most of the time. Fuel leaks are quite rare and usually occur only when the boat is severely damaged, and are so fast that you run out of fuel in a matter of minutes, or hours at most, not days.