I did a search on Fold3.com (great web site!) and found several references to U.S.E.D. It appears that this relates to some civilian engineering function. There are muster rolls showing various trades people (carpenters, welders, etc.) being assigned to ships and stations. The ships were typically barges, tugs, drydocks, etc. Several ships had designations such as USED ##, whee ## was a 2-digit number.

Still not clear what USED stands for.