A puzzle

from "Amusements in Mathematics" by Henry Ernest Dudeney (Author of "The Canterbury Puzzles: and other curious problems", etc) Pub Thomas Nelson and Sons, 1917.

For those on anchor watch on the Thames tonight: especially D. who has heavier vessels upstream and insecure.

I think it was on a night sail off Portland Bill that someone else shared the wonderful story of a gallant NATO ally (the losers at Taranto, if I remember rightly) in a large deployment in heavy weather at Halifax, Nova Scotia. They signalled the rest of the fleet to check their anchors as they all seemed to be dragging. And curiously, they all seemed to be dragging into the tide.

Someone tactfully found the words to suggest that there was a different scenario, in which only one vessel needed to take action, ideally with little delay.