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If I interpreted this correctly, a seazone containing both submarines AND transports blocks the movement of sea units. This doesn�t make any sense.
Do submarines have the ability to protect allied transports? (obviously not from air units)
Can you ignore making an attack on a seazone containing transports and submarines to make a seashore bombardment?
Don’t forget:
@rulebook:
An enemy submarine and/or transport does not block any of your units’ movement, nor does it prevent loading or offloading
in that sea zone (with one exception - see Special Combat Movement: Transports, pg. 13). As the moving player, you have the
option of attacking an enemy submarine and/or transport that shares a sea zone with you. However, if a warship chooses to sink
an unescorted transport, that warship must end its movement in that sea zone. It is possible that some units may stop to attack
while others continue moving through the sea zone.
This should answer all your questions.