"Swamp Angel" sans cannon which is shown to be on public display in
Trenton, NJ. It exploded and investigated by Franklin Institute
hearings.

It's not like we had found the cannon there, but the Parrott gun
platform on top of criss-crossed wooden grillage in closed association
with over 600 used brass friction primers. The grillage was of an
undetermined depth, though geophysical reporting stated that bedrock
was at 70' [feet] below the then current elevation of the marsh in
Foundry Cove. It was under the remains of the numerous large concrete
stanchions (two people could stand on one) of the "Chicago Steel and
Bridge Co." huge "Bridge Shop" which burned in Dec. of 1912,
destroying is assembly line. They're still in business last I heard a
"gravity wave" experiment built by them in the Midwest.