Definition of "gateman"

The cars built before 1913 had clerestory roofs, after the American style, and also were provided with gates and end vestibule platforms requiring gatemen.

1951 January, “The Inner Circle and its Rolling Stock”, in Railway Magazine, page 59

The carriages - or cars - had gated platforms at the end, where 'gatemen' stood and controlled the flow of passengers on and off the trains in the absence of automatic doors. […] When each gateman had secured his doors and gate, he rang a bell, then the conductor rang his bell as the signal for the driver to set off.

2012, Andrew Martin, Underground Overground: A passenger's history of the Tube, Profile Books, page 147