German destroyers appeared one night later on off the North Foreland and opened fire, which was returned by the monitor and the shore guns.

The enemy immediately withdrew, and never appeared again in 1917 in this neighbourhood.
Meanwhile efforts had been made to increase the strength of the Dover force, and by the end of June it stood at 4 flotilla leaders, 29 modern destroyers (including "Tribal" class), 10 old 30-knotters, and 6 "P" boats.

The increase in strength was rendered possible owing to the relief of destroyers of the "M" and "L" classes at Harwich by new vessels recently completed and by the weakening of that force numerically.

The flotilla leaders were a great asset to Dover, as, although they were coal-burning ships and lacked the speed of the German destroyers, their powerful armament made it possible for them to engage successfully a numerically greatly superior force.

This was clearly shown on the occasion of the action between the _Broke_ and _Swift_ and a German force of destroyers on the night of April 20-21, 1917.
The flotilla leaders on that occasion were, as was customary, patrolling at the Dover end of the cross-Channel barrage.