Thanks, Stephen, I'd entirely missed the fact that all units are able to move and attack a second time in the mobile move/combat phase.
This also (I think) explains the first errata which I have seen on other threads.
IWO ERRATA as of 2015.11.16 (no error in CRT)
13.0 Modifications to Standard Rules
(clarification) During the Mobile Movement phase of a storm turn, all MA are reduced to 1.
If the movement allowance (MA) is reduced to half in the mobile movement phase and the storm reduces it again to half (rounded down) then it will indeed only be 1.
So given that all the units have an MA of 6, I think I understand the turn structure better now.
All units move with an MA=6 (bearing in mind various restrictions regarding such things as beach landings and EZOC)
All attacks are declared and fire support tokens allocated to various targets. On a roll of 1-3 the target is suppressed. All combat is resolved.
All units move again with an MA=3
All units attack again but without fire support.
Storm. (as above except)
Units move with MA=3
Targets are suppressed on a roll of 1-2
Units second movement (mobile movement) is with MA=1 (i.e units may only enter clear or beach hexes)
This will certainly make life a little easier than only moving and attacking once per turn.