A transport can load units while in any friendly sea zone along its route, including the sea zone it started in. If a transport loads
land units during the Combat Move phase, it must offload those units to attack a hostile territory as part of an amphibious
assault during the Conduct Combat phase, or it must retreat during the sea combat step of the amphibious assault sequence
while attempting to do so. A transport that is part of an amphibious assault must end its movement in a friendly sea zone (or
one that could become friendly as result of sea combat) from which it can conduct the assault. However, a transport is not
allowed to offload land units for an amphibious assault in a sea zone containing 1 or more ignored enemy submarines unless at
least 1 warship belonging to the attacking power is also present in the sea zone at the end of the Combat Move phase.
Page 16, AA Pacific 1940 Rulebook
Battleships, aircraft carriers, cruisers, destroyers, submarines, and transports move, attack, and defend in sea zones. They
can’t move into territories. For the sake of these rules, the following are surface warships: battleships, carriers, cruisers, and
destroyers. Transports are not warships. Submarines are warships, but they are not surface warships.
Page 31, AA Pacific 1940 Rulebook
This might help clarify.
