One of the first instances of this in a major assault was for HUSKY. In planning the operation it was realized the beaches were too shallow and the vehicles would have to wade some 150 to 200 feet though water up to ten feet deep. The solution developed was to load aboard sections of "naval lighterage pontons" (developed in 1939 and tested 1940-1941), which then were assembled as a floating causeway some 175 feet long. The NLP were also the basis of the Rhino Ferry, which was simply NLP sections bolyed together as a raft with outboards, which could be towed by a LST, further increasing its useful load and also available to act as a causeway when needed. I suspect that was the impetus for development of the Newport design. The question of course is why they felt it was necessary to have it as a permanent part of the design, since using NLP when necessary...or just building extempore bulldozed causeways, was a more flexible solution.