Giant ships cannot enter shallow waters and when they do, they become Concordia. In order to get to them, you either have to take a ferry or there must be a pier that connects the mainland to the point where the ship is anchored. This is what civilians do, trust the guys from the armed forces to do things in their own unique daredevil style.
The LRO (Land Rover Owners International) spent a day with 40 Commando, The Royal Marines, 11 (ATT) Squadron, Instow, Devon, sometime in 2008. One of the members of that squad drove out to the landing craft and back, first as co-driver with a trainer and then as driver. The water was 1.5-metres deep by the landing craft with waves occasionally breaking over the vehicle, yet the Landrover was back on Terra-firma after wading into the sea. The video is pretty old and grainy, however, nothing beats watching a Landrover driving into the sea trying to part it into two.