The destroyers which were engaged during daylight hours in this work, and those patrolling the barrages across the Straits and off the Belgian coast, obviously required some rest at night, and this fact reduced the number available for duty in the dark hours, the only time during which enemy destroyer attacks took place.
Up to the spring of 1917 the examination service of all vessels passing the Straits of Dover had been carried out in the Downs.

This led to a very large number of merchant ships being at anchor in the Downs at night, and these vessels were obviously open to attack by enemy craft of every description.

It was always a marvel to me that the enemy showed such a lack of enterprise in failing to take advantage of these conditions.

In order to protect these vessels to some extent, a light cruiser from Dover, and one usually borrowed from Harwich, together with a division of destroyers either from Dover, or borrowed also from Harwich, were anchored off Ramsgate, and backed by a monitor if one was available, necessitating a division of strength and a weakening of the force available for work in the Straits of Dover proper.
The result of this conflict of interests in the early part of the year was that for the patrol of the actual Straits in the darkness of night on a line some 30 miles in length, the number of vessels available rarely if ever exceeded six--viz.

two flotilla leaders and four destroyers, with the destroyers resting in Dover (four to six in number) with steam ready at short notice as a reserve.
An attack had been made on the Dover Patrol in October, 1916, which had resulted in the loss by us of one destroyer and six drifters, and serious damage to another destroyer.