This is the kind of equipment found in the Pacific theatre, especially Japan -- there's lots of 50 Hz there right outside the base.
Back in the day, rotary phase-converters for 400 Hz aircraft power were common as dust. They used additional poles within a motor-generator scheme to bump the frequency. It'd take the whole output of this XFMR to drive the load of a big aircraft while it's on the tarmac.
Now VFDs have made them out-dated.
Interesting to note the various tap options on the primary.
