The ‘Riverboat’ model appears in the early ’60s Feather Craft catalogs. While not exactly the same hull form, it looks quite a bit like a Hickman Sea Sled. Not a special government project, but sold as a regular boat. Probably not lots of them made though.
The military ‘boat’ you’re thinking of is probably this:
They weren’t intended to be used primarily as boats, but two of them could be attached together to form a pontoon for a floating bridge. More info and pics here, and some even better pics in the threads Mike linked above.
I’d love to find a Riverboat in restore-able shape.