@midnight_reaper yes. It helped me a lot. One clarification about my first query. The same applies if on that battle there wanst a destroyer? E.g. UK has the carrier and a fighter, while the Germany has a sub and a fighter. So Germany hits the carrier and the UK doesnt hit a unit on first round of battle. Germany decide to retreat. So subs can retreat by moving on next sea zone? I am asking because, now there is not a destroyer. And subs cant hit the plane, so maybe they cant retreat in another sea zone and only the fighter can move and land on another territory?
When units retreat, either land units on land or naval units at sea, they must retreat to a territory where at least one of the land or naval units moved from during combat movement. (Land units doing an amphibious landing are not allowed to retreat, but that is outside the scope of this question.) In your case, you have 1 submarine and 1 fighter. To end this fight, you have 2 options: retreat or submerge submarine, then retreat.
Retreat: You can retreat as I outlined in my last answer. If you choose to retreat, then you can only retreat to SZ 9 or SZ 15, depending on whether your submarine came from SZ 9 or SZ 15 to attack SZ 14. Your fighter would still hang around until non-combat movement, as discussed previously. What you can not do is retreat your submarine to any other sea zones. You must retreat from whence you came.
Submerge Submarine: If you feel you must retain control of SZ 14, where the combat took place, and you feel like trying your luck against the defending fighter one more time, then you can submerge your submarine instead of retreating. When you submerge a submarine, it quits the fight but doesn’t leave the sea zone. Because you have to start another round of combat in order to submerge, your fighter would have to stay and fight 1 more round before calling off the fight. While this would give you the opportunity to finish off that British fighter, it would also give the British another chance to kill your fighter. See page 16 for submerging in combat and page 27 for submarine-specific rules.
In your specific case, I would retreat instead of submerge if it was me. But now you know what I think your options are.
My 2 IPCs,
Everything is clear now. Thanks a lot for the detailed info