Amtraks were used quite extensively in the Pacific in WWII. These were tracked amphibious vehicles--the name comes from amphibious tractor. There were a number of versions, but they all featured tracks much like tank tracks and were very handy in assaults on locations that featured a coral reef. Unlike the LCVP (or Higgins boats, the iconic landing craft of WWII) the Amtraks could wade right up to a coral reef, climb over it, go right to the beach and deliver its troops directly to the land.

This was an obvious boon to American troops, but there were costs as well. Early versions--such as the ones used at Tarawa--had very light armor and were open-topped. Many were disabled and destroyed during the assault, and many of the men being transported and those operating the vehicles were injured or killed by enemy fire. A lack of armament to suppress or destroy beach fortifications was rectified in later models, and some of these were used inland much like tanks. By the time of the Battle of Okinawa, there were hundreds being used in each assault.

Also note that Amtraks were used for a number of river crossings in the European theater as well.

The other famous amphibious vehicle used in WWII was the "Duck." With the designation of DUKW (D for designed in 1942, U for utility, K for a powered front axel, and W for six powered wheels), the Duck was a truck modified with flotation devices and a propeller for water movement. Logistically, these trucks were a godsend. They could be loaded up at sea and then swim and drive directly to where they were needed. However, they were hideously vulnerable to any kind of enemy fire, as they were unarmored. Basically they were kept from heavy combat and were used for transport.