I found in the O.R. the earliest mention of "thunder-barrels" was the modified defences of Fort Moultrie by Andersons forces. They had placed "thunder-barrels" at each of the Fort's angles. The Dutch "donderbus" translates to "thunder-barrel", the same device called "blunderbuss" by the English according to what I can find, but I don't see how that relates to the Civil War reference.

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David Upton