Some coastal radio stations like ITT Mackay New York City WSF ran MCW on their working frequency but they were very few in number became MCW was very broad about 2 kHz wide if you include harmonics.
A2 MCW was kept to keep compatability with Type B emission, Spark. Old auto alarms originally only responded to modulation and would be triggered by the modulation of a spark signal but not an ICW or an Interrupted (that is "keyed") Continous Wave signal. Later autoalarms responded to MCW and CW signals.
Some ships had crystal radio receivers with fixed tuning for 500 kHz used as yet another backup receiver for use in an emergency. These receivers only received Spark and Modulated Continuous Wave MCW or IMCW Interrupted Modulated Continuous Wave (A2) signals.
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David Ring N1EA