Dear Bernard
This paper might be of interest to read. The US was one of the key suppliers of Grain to Wellingtons Army in the Peninsular. Its amazing that the US decided to carry in feeding an Army of a Country they were about to declare war on. It shows Wellington was really worried about what would happen if they had stopped the supply https://www.napoleon-series.org/military-info/Warof1812/2006/Issue5/c_Wellington.html
Geraint