Just to add to whats been said so far ...... save a few times during a patrol ... be on the surface and at normal speed ... make a save ( be sure to hit the enter key after typing what to call it ) and then click the save word .............. I generally save about 3 to 4 times during a patrol .... I name them like " got two " ... " convoy " .... " iamborded " .... " homeward " ..............
When you load up the game again you'll see the saves you named and can start from there if you so desire ( but you lose anything afterward ) .......
Reason I always save ... its a bummer to have an almost perfect patrol and I am so proud of my crew .... then the power company decides its time to work on the power lines and cuts it off