I should like to make some comment on Captain Wylie's article in the January issue of the Journal (18, 27). While not disputing his arithmetic I should like to state that in practice true motion is much more effective than he implies. For two years I used an Escort true motion set on the Southampton, Cherbourg, New York run and I can say most unequivocally that ships did not have to be proceeding at 18 knots to get satisfactory trails on the 12-mile range scale. In fact one could see useful trails when ships were proceeding reasonably slowly.