In red is the refuel area for the first side mission U-boat blitz
for mission complete - you must meet the milkcow
when you are a distance away (cant remember how far) the mission is complete
To refuel you must get close (50m)
and then you get the option to resupply.
Once you are within the mission pass area - the milkcow may head away so catch it before it does.
The yellow areas are where the main campaign milk cows are.
Use radio man to call resupply.
If ok you will get a new side mission to meet milkcow in one of those areas