There! you see how easy this one is going to be. All the questions are answered correctly by the team of Terry C. and George Gaskill. Thanks guys! The only thing we do not know for sure is whether it was a Planer or Shaper which was used to machine the material between the Trunnions which turning operations on a lathe could not reach. Mike and I believe that Terry was correct in his pick of a shaper. George has shown what a much less common, these days, Planer looks like and also pointed out that there is a straight sided part, (tapered or cylindrical), in the Rodman Gun's profile.
Our rationale for our vote for the shaper is the fact that it would be infinitely more difficult and expensive to buy or build a Planer to do this "Tickling the Belly of the Beast" work where very little metal is actually removed. Can you imagine how large and heavy, (200,000 to 500,000 pounds) a Planer would have to be to accelerate AND decelerate all 50,000 pounds of this massive tube? The shaper, by contrast is relatively easy to modify to do this work, in that only a longer stroke and a longer ram would have to be incorporated. The tube does not have to reciprocate under the tool at all. The ram with the lathe-tool and clapper box reciprocates over the massive tube which is held in a robust set of centers so it can be rotated under the shaper's cutting tool.
Thanks again fellows,
Tracy and Mike
P.S. This is our small shaper we use for making internal slots in retaining rings, collars, splines, etc. with a 6" stroke. The slot on top of the ram is 8" long. The clapper box and lathe/shaper cutting tool is over the work held in the vise. It's a lot of fun to watch this machine work with all the rotating parts, eccentric moving parts and reciprocating parts. When in action, it makes you think more of a "Merry-Go-Round" or Carosel than a machine tool. With automatic side feed and reciprocation it can flatten a 6 X 6 piece of steel w/.010" depth of cut in short order, (less than 5 minutes). These go for $300 to $500 on ebay where we got ours.