Unescorted and poorly escorted convoys, Atlantic, 1940

Ships which sailed in convoy were of necessity limited in their speed to that of the slowest vessel in their midst. There was also a shortage of vessels to escort the convoys which were capable of antisubmarine operations should they be attacked. The decision was made to assemble the large convoys and sail them unescorted, or under-escorted, because Great Britain lacked the means of feeding itself or providing enough fuel for its needs. One example of the regrettable effects of the decision can be found in Convoy SC-7 (SC refers to Slow Convoy) which sailed from the port of Sydney, Newfoundland, bound for Liverpool, in October 1940 comprised of 35 ships.

SC-7 was limited to less than eight knots in speed, and escorted by a single sloop. The slow rate of steaming irked many captains of faster vessels, and the convoy became strung out during the crossing. As it reached the Western Approaches near Ireland additional escorts became available, but the convoy was so separated that defending it was nearly impractical. Of the 35 ships which departed Sydney, twenty never reached their planned destination, instead succumbing to the German U-boats. Nearly 80,000 tons of shipping were lost, along with their crews and cargoes. The decision to risk running the U-boats in slow, unescorted convoys nearly brought England to lose the war due to attrition, and forced the intervention of the Americans in order to protect the ships and their valuable cargoes.