Convoy in Bedford Basin, Halifax, April 1,1942. Department of National Defence / National Archives of Canada, PA-112993.

There are two main reasons for grouping ships in a convoy: first of all, over such a wide area as the Atlantic Ocean, a single group of some forty, tightly packed ships is harder to locate than several, scattered crafts. In addition, the number of warships required to protect a convoy is obviously much lower than what would be needed if every single ship had her own escort.

The convoy system had proven itself to be a valid concept during WWI. When the war broke out in September1939, shipping by convoys was rapidly organized. The first convoy, HX-1, sailed from Halifax on September 16th for an uneventful crossing. As war went on, convoys got to be more frequent and larger. The largest of all, HXS-300, was made up of 167 ships.

Great Britain required a very wide range of goods. Troops had to be carried overseas as well as all kind of military equipment - tanks, various types of vehicles, fuel, weapons. Food, lumber, building materials for barracks, and raw materials for the industry also came by boat. Plus all those goods that were already the object of a regular trade between the British Isles and North America before the war.

Convoy Organization
The faster a ship can cross the Ocean, the less risk she runs of being sighted and attacked by U-boats. But a convoy cannot be faster than its slowest member. The earlier convoys were too fast for older ships, which had to strain their engines to keep up with the other freighters. The slightest mechanical problem forced them to pull out of the convoy, thus becoming an easy target. To solve this problem, a two-speed system was implemented: fast convoys were still formed in Halifax harbour, but, starting August 15th, 1940, slower convoys regrouped in Sydney. In 1941, fast convoys left every six days and made the crossing to Great Britain in 13 or 14 days. Slow convoys left every six days as well but took up to 16 or 17 days to sail across the Atlantic. The meeting point was moved south to New York in September 1942.

Cruising Order of fast convoy HX-202, August 1942. It includes names of ship, countries where registered, cargo, and port of destination. Canadian War Museum, 198700068-008

The forty - or so - ships that make up a convoy are positioned within a grid: there are nine columns, 920 metres apart, and in each column five ships, 550 metres apart. Ships carrying dangerous cargoes, such as gas, fuel, explosives are placed in the centre, the position that affords the most protection against enemy torpedoes. A convoy commodore, in most cases a retired naval officer, is on board one of the merchant ships to take defensive measures as required and ensure coordination with the escort.

Naval authorities select the route, avoiding concentrations of U-boats, which crisscross the Northern Atlantic. Once the convoy has sailed off, it is joined by destroyers, corvettes and frigates, which position themselves on the periphery. A command ship precedes the convoy, while other escort ships take place on the flanks and astern of the convoy, in order to form a screen against submarines. Escort ships must keep their relative positions while making zigzags that allow them to sweep as broad an area as can be with the ASDIC detection system. At the end of the route, merchant ships leave the convoy in a pre-set order and continue towards their final destination, whether in England, Scotland or Northern Ireland.

Position of merchant ships with escort made of a destroyer and three corvettes.