Here are the links from the U.S.N.G. Each will open up in a new window.
Once you are on the Mission Manager site, there will be a 'Coords:' dropdown where you should select 'USNG'. At the top, make sure the 'Grid' checkbox is selected. From that point, you can zoom in up to a 100m grid. The pointer can provide 1m coordinates.
Convert Lat/Lon to USNG
Mission Manager mapping site.