Jane,
Yes. The US Army did have ships and vessels pre WW II. Just not so many. The Corps of Engineers for instance maintained waterways in the United States. They had their own fleet of vessels. They were also responsible for landing craft, engineering works adjacent to, and over, waterways etc.
Most army boats/ ships were small items; the odd landing craft, river boats, tenders etc. There were also cargo ships controlled by the US Army for supplying garrisons.
The Army Transportation Corps was started in July 1942. The 24 Hospital ships, for example, became hospital ships 1943, 1944 or 1945. The ATC had many other vessels as well