The convoys all put into Lerwick, in the Shetland Islands, both on the eastward and westward passages, so that Lerwick acted as a junction for the whole system.

From Lerwick, convoys to Scandinavia left in the afternoon under the protection of two or three destroyers, and, with some armed patrol vessels in company up to a certain stage, made the Norwegian coast at varying points, and there dispersed, and the destroyers then picked up the west-bound convoy at a rendezvous off the Norwegian coast shortly before dark, and steered for a rendezvous between Norway and the Shetland Islands, where an escort of armed patrol vessels joined the convoy at daylight to assist in its protection to Lerwick.

From Lerwick convoys were dispatched to various points on the coast of the United Kingdom; those making for southern ports on the East Coast were escorted by a force composed of some of the old "River" class or of 30-knot class destroyers, and trawlers belonging to the East Coast Command based on the Humber, and those making for more northerly ports or ports on the West Coast were escorted merely by armed patrol vessels, as the danger of submarine attack to these convoys was not so great.
The main difficulty was the provision of the destroyers required for the proper protection of the convoys, and to a lesser degree the provision of armed patrol vessels of the trawler, whaler, or drifter types.
The conference held early in April, 1917, had reported that whilst stronger protection was naturally desirable, the very least force that could give defence to the convoys between Lerwick and the East Coast ports would be a total of twenty-three destroyers and fifty trawlers, whilst for each convoy between Lerwick and Norway at least two destroyers and four trawlers were needed.

The destroyers for the latter convoys were provided by the Grand Fleet, although they could ill be spared.

The total number so utilized was six.