Many thanks for all those great comment !!!
praga, when you're on the defensive you can stockpile all the supply you need where your troops are located, but when you're on the offensive it's very important to have a good supply line to carry fuel, ammo, food, more troops and vehicules.
It take time to make round trips between the beach and the boats with LCVP (to carry troops) and LCM (to carry tanks), once the beach is safe it's better to use bigger landing ship like those LCT-6 if you don't want to see your troops stuck around the beach, awaiting the supply to continue the offensive. the Dukw (amphibious trucks) also do a great job for this purpose.
You can see on my work in progress how I built them, they're made by Armageddon, a french manufacturer, not an easy model but the result worth it.
Right now I'm collecting what is necessary for my next big project.