Its narrowness at various points, such as the Straits of Gibraltar, the Malta Channel, the Straits of Messina, and the passages to the AEgean cause such convergence of trade as to make it a very simple matter for a submarine to operate with success.

Evasion by change of route is almost impossible.

Operations designed to prevent the exit of submarines from the Adriatic were difficult, because the depth of water in the Straits of Otranto militated against the adoption of effective mining and the laying of an effective net barrage.
For the above reasons the Admiralty was always very averse to the sending of a large volume of our Far Eastern trade through the Mediterranean, and strongly urged the Cape route instead; but the shortage of shipping, combined with the increased length of the Cape route, influenced the Ministry of Shipping to press strongly for the Mediterranean as opposed to the other route.

A "through" convoy from England to Port Said was started in October, and by the end of November two ships had been sunk out of the thirty-five that had been under convoy.

The return convoy; Port Said to England, was only started in December.
The losses of British merchant steamships per quarter in the Mediterranean during 1917 is shown below: Quarter ending June 30 69 September 30 29 October and November 28 It is impossible to close this chapter describing the convoys without mention being made of the fine work accomplished by those upon whose shoulders fell the task of organizing and working the whole system.