Its a common misconception, and one perpetuated by our esteemed MSM. Many times we would be interviewed by a reporter about a mission here in the States, and plainly state we were US Army Transportation Corps and the vessel was a US Army LCU.
When the articles appear in print or the local news show, they invariably referred to us as Corps of Engineers and the LCU as a Corps of Engineer barge.
Blaming it on the media works for me.
U.S. Army: We're better then the media says we are.