@suprise:
Do enemy subs stop the ability of transports from loading during an amphibious assult
@GeneralHandGrenade:
Yes if they are in the same zone as where you are trying to load them.
@weddingsinger:
They preventing loading and unloading, right?
The presence of an enemy submarine does not make the seazone hostile. So the transport(s) may be loaded during Combat Move Phase.
But it/they must be offloaded for an amphibious assault then.
@GeneralHandGrenade:
They prevent unloading if they are not accompanied by a surface warship. If you have the warship you can either ignore the sub or kill him and then drop the land units off.
Not necessarily a surface warship. Any warship escorting the transport(s) at the end of the Combat Move Phase is fine for offloading the transport(s) despite the presence of ignored enemy submarines.