And now for something slightly bonkers: The "Nuclear EEL", a 1969 proposal for a 1400*38ft, 40-50 knot shallow diving (200ft) nuclear powered train ferry for trans-oceanic cargo routes. Extensive use of concrete for permanent ballast, and un/loading performed by hauling the thing part way up a ramp and opening the nose. Being right before containerisation took off, the author focuses on the ease of cargo handling in rail ferries compared to the general cargo ships then in use.
Reference: Whitelaw, RL, "The Nuclear EEL", Mechanical Engineering Nov. 1969.
RP1's comment: Given how much time was spent in handling cargo, pretty much any kind of modularisation; container, rail, barge, was much cheaper. In engineering terms however this thing is bonkers. The L/D ratio is so far off the charts I could only guess what the power required would be. Depth control at speed would be a nightmare - a five degree angle means the bow and stern are 120ft different in depth.