@Tizkit
Carrier B must move there to provide a landing space for the surviving fighter.
From the rulebook, Pacific 1940.2, page 22
Aircraft carriers can move to sea zones to allow friendly
fighters and tactical bombers to land. They must move there,
range permitting, if they didn’t move in the Combat Move
phase and the friendly sea zone is the only valid landing zone
for the air units. An aircraft carrier and a fighter or tactical
bomber must both end their moves in the same sea zone in
order for the air unit to land on the carrier.
The requirement during Combat Movement simply is:
Rulebook Pacific 1940.2, page 13:
A fighter or tactical bomber can move its full 4 spaces to attack in a sea zone instead of saving movement, but only if a carrier could be there for it to land on by the conclusion of the Mobilize New Units phase.
So concerning your follow up question: Yes you can move Carrier B during Combat Move Phase. But you must comply to the rules for Combat Movement of course, which would for example mean that this carrier has to end his Combat Move in a hostile seazone, participating in an attack there.
HTH :smiley: