battle of the atlantic

During WWI, it was found that fewer merchant ships were sunk when traveling in well-guarded convoys whose courses were randomly changed.

Convoys became even more important during WWII as the German air and submarine services became better at locating ships. The most dangerous times for convoys, or ships for that matter, wasn't at mid-ocean. Both exit and entry ports were limited in number, so surveillance was made much easier. Other choke-points along the routes to Soviet ports were also carefully watched. Once a ship, or convoy location was identified an attack would be made. To get past the escorts, the German's used combined attacks by wolf-packs and/or aircraft. These attack became increasingly ineffective as Allied ASW techniques improved. We had their codes, long-range aerial patrols, and sonar all combined to reduce sinkings.

Re: battle of the atlantic


Ask yourself, what would be easier to find in a big ocean: any one out of 100 dots that are spread out, or one slightly larger dot (made up of 100 small dots).

Having ships sail in convoy makes them in fact harder to find and it makes it easier to protect the ships.

From wikipedia:

On the entry of the U.S. into World War II, the U.S. Navy decided not to instigate convoys on eastern seaboard of the U.S. Fleet Admiral Ernest King ignored advice on this subject from the British as he had formed a poor opinion of the Royal Navy early in his career. The result was what the U-boat crews called their second happy time, which did not end until convoys were introduced. It lasted from January 1942 to about August of that year. German submariners named it the happy time or the golden time as defence measures were weak and disorganised, and the U-boats were able to inflict massive damage with little risk. During this second happy time, Axis submarines sank 609 ships totaling 3.1 million tons for the loss of only 22 U-boats. This was roughly one quarter of all shipping sunk by U-boats during the entire Second World War, and constituted by far the most serious defeat ever suffered by the US Navy. This was, unfortunately for the Allies, as near to a laboratory test as is ever seen in war time and it proved conclusively that convoys worked.

Actually, origianally convoys of merchant ships were formed as a protection against pirates.
Since the 17th century, neutral powers have claimed the "right of convoy"; that is, immunity from search for neutral merchant vessels sailing under the convoy of a warship of the neutral.
Great Britain was one of the very few countries, who didn't recognise this, and only deviated from its position during the Crimean War in order to harmonize its practice with that of its French ally.

In the Declaration of London (1909), the principal powers, including Great Britain, recognized and formalized the right of neutral convoy. The London declaration failed to enter into force, however. During World War I the right of convoy was invoked on only one or two occasions.



(photo above publishe in The Sunday Telegraph, 08.07.07, page 14)

The point about finding a single convoy in a huge ocean is well taken. Additionally, convoys allowed the three navies involved, the Royal Navy, the Royal Canadian Navy and the United States Navy to provide protection. Land based aircraft could cover a good deal of the range of the convoys which usually assembled at or near Halifax, Nova Scotia. From there, they made a run to the vicinity of Iceland, where land based aircraft were again available to search for and attack submarines. From Iceland to the Irish Sea, there was only a very small corridor in which the Allies could not rely on land based aircraft to find and attack submarines, and with the entry of the United States into the war, the long-range PBY Catalina made it possible to search for submarines in all but a very small area of the convoy corridors. PBY stands for Patrol Bomber, with the "Y" designating that it was manufactured by Consolidated Aircraft Corporation. As a naval bomber, they were not very effective--but finding and tracking the submarines was an extremely important mission, which they performed to perfection. (In the Pacific, PBYs were painted flat black, and were used very successfully to attack Japanese ships at night--but attacking a submarine successfully is a much more difficult mission, the target is much smaller, and it is nearly impossible to find them and attack them from the air at night.) Nevertheless, PBYs did attack submarines, and are credited with 40 kills. The first PBYs were delivered to the RAF in 1941, and a PBY, with an American at the controls (a "training officer") helped to find Bismarck in 1941. The PBY was manufactured under contract by Vickers in Canada, and was used by the United States, the United Kingdom, Canada, Australia and New Zealand. The PBY was crucial in the naval war which centered on the convoys who steamed to Murmansk to supply the Russians.

Most heavy losses occurred when the Germans located a convoy, and attacked in "wolf pack" fashion, with many submarines alerted to the presence and course of the convoy and guided to the target by continuous short-wave radio broadcasts from Germany. The submarine which found the convoy would not attack, but would radio the position, and regularly drop off the course of the convoy (to avoid the escorts) to continue to broadcast the position of the convoy. The other submarines in the wolf pack which attacked would maintain radio silence, and would wait for nightfall if possible so as to attack on the surface (more effective) while listening for the broadcasts which pinpointed the position of the convoy. This meant that some convoys were devastated, while others steamed uneventfully to their destination.

Of the three navies, the Royal Canadian Navy by far was the workhorse of the Atlantic convoy system. The Canadians escorted more merchant shipping than the Royal Navy and the United States Navy combined. Because of the difficulty of getting ships from the Great Lakes ship yards to the Atalantic (there was no St. Lawrence Seaway at that time), the RCN relied principally on minesweepers and corvettes for their excort ships, and it was a hellish service they put in. The Canadians did eventually build destroyers in the Québec shipyards, but whenever the RCN produced a new destroyer with an efficient crew, the Royal Navy usually snapped them up for their "hunter-killer" groups which hunted down submarines, or they were put on patrol in the English Channel and the Bay of Biscay, where the Royal Navy fought it out with German "E-boat" patrol boats and hunted submarines leaving or returning to their bases on the coast of France. The Canadians designed a ship longer than a corvette and smaller than a destroyer, and dubbed it a "frigate," although their frigates did not reach the convoy service until late in the war. They sold many of their frigates to the United States Navy and the Royal Navy, as well as frigates being manufactured under license in the United Kingdom and the United States. By the height of the "Battle of the Atlantic," the convoys were assembled and controlled by the RCN from Halifax. At the end of the War, the Canadians had the third largest navy in the world, after the USN and the RN.

An escort vessel, even the lowly minesweeper, could be very effective against submarines. Although, obviously, they wanted to sink submarines, their principal task was to make the submariners "keep their heads down." A merchant convoy necessarily moves at the speed of the slowest ships (the Americans built special "fast" cargo vessels for use in the Pacific), which often meant that the convoy moved at 8 knots or even as slowly as 6 knots. Even a submerged submarine can exceed that speed running on batteries, so the escort vessels need to force them to dive, and to keep them down long enough for the convoy to escape. Therefore, the Germans tended to concentrate on a single convoy they had located, and to send in more submarines then there were escort vessels. The Canadians had an ugly war as a result, since their destroyers and frigates were usually taken by the RN almost as soon as they were commissioned, and they continued to rely upon the lowly corvettes and minesweepers. The spectacular successes of the u-boat wolf packs tends to mask the fact that most convoys made it to England without being attacked. With the Canadians doing most of the escort duty, and organizing the convoys, the USN and the RN concentrated on killing u-boats--and the were eventually very successful. Three out of four submariners in the German Navy sooner or later failed to return from patrol. The only other single Allied service which suffered as heavily was the United States Army Air Force which conducted daylight bombing raids over Germany and Austria.

With the success of the convoy system, and the hunter-killer groups, u-boats began to boldly go into the coastal waters off Halifax and even into the huge estuary of the St. Laurent River. There, the ASW equipment of the Allies, what we think of as "sonar" was far less effective because of the varying currents--dense, cold water could bounce a signal back and u-boats took advantage of this to get in close to the convoy assembly areas. The "Battle of the Atlantic" lead both the Americans and the English to invest heavily in ASW equipment, and, after the war, to eventually put listening devices on the floor of the ocean.

Source


And not to forget that the Germans had convoys as well ...