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Is there no such thing as a brushless (i.e. electronically commutated) motor at this scale? This is basically diesel-electric we're talking about? I Imagine the electronic controller would cost huge $$$ but would be far more efficient in the long run.

Right. But (a) these vessels are government-owned and -operated, so there's no competitive pressure, and (b) they need a lot of reliability on these engines.

One of the YouTube videos of the MV Walla Walla shows that they use the forward-facing engines for breaking in the last few seconds before the vessel docks. They need those motors to spin up or reverse direction in just a few seconds, and it's a life-and-death thing. Maybe they feel that sticking with technology that's ancient but foolproof is a better way to go.

It sounds like these motors are like the motors that are used in elevator drives, only scaled way up. Motors of that type have to be able to deliver very stable operation down to fractions of an RPM, deliver high torque at low RPM, and be very very reliable. I've noticed that elevator motors have large commutators (large compared with the rotor diameter) like the motors on the MV Walla Walla.