Thanks Bob, very interesting. There are only a few large Brooke guns surviving so this will be a welcome addition. Since this is fresh water and mud, the guns and their markings should be in very good condition and we can take the Brooke numbers, look in the Tredegar foundry book (assuming they were made at Tredegar) and see when they were shipped etc. The Dahlgren was probably one of many captured at the Gosport VA Navy Yard in 1861, but we'll be able to use the numbers to track where that gun was pre-war.
I think the same river already gave up a new-condition US bronze 24-pounder field howitzer. A fisherman found it in shallow water sometime back in the 1950's or so. I could have my Pee Dee rivers mixed up, there are a couple with similar names. The story of that recovery is in Warren Ripley's excellent book. Anyone who has any interest in CW artillery needs that book in their library, it should be very inexpensive online now as it has been in print for a very long time.