How separate were American and British landing-craft designs?

How did American landing craft compare with British designs?

They were often the same or closely related because British and American officers observed, ordered, and adapted designs from one another.

Many types were common to both services because officers watched one another's experiments and sometimes placed orders around the same designs. The Higgins examples show reciprocal observation rather than a one-way transfer. The US Marine Corps did substantial interwar amphibious work, though the exact balance of design leadership remains unresolved. Simple national invention stories miss how often Allied officers circulated and adapted one another's work.