In the 1930s, how was refrigeration handled in trains' dining cars?

Question

Possibilities would seem to include: Simple ice boxes; dry ice; mechanical refrigeration.

Answer 1

The good old fashion ice box.  Ice was also used in refridgerated freight cars, commonly called reefers (no, not that kind of reefer).

Mechanical refridgeration came much later.

Answer 2

My guess would be the ice box.

Answer 3

blocks of ice picked up at the station and put on the train