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  The Convoy System <<<
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Books by John Barratt


Armada 1588


The Battle of Marston Moor


The Civil War in South-West England 1642-1646


Cavalier Generals

The Convoy System - Origins
The Convoy System - Origins
by John Barratt

The convoy system, which can be defined as a group of merchant vessels sailing together, with or without naval escort, for mutual security and protection, has a much longer history than sometimes suggested. It was commonly employed during the Age of Sail, notably by British vessels under threat from French and US commerce raiders, and indeed probably has its origins in ancient times.

However on the outbreak of World War I in 1914, it was widely argued that the advent of steam had rendered the convoy obsolete. It was felt that the necessary delays involved in assembling vessels into convoy would take up too much time, as would the limitation of a convoy's speed to that of the slowest ship. Many captains argued that such a concentration of shipping would bring with it an unacceptable risk of collision, as well as presenting an easy target to submarine attack. The British Royal Navy felt that escorting convoys was too "defensive" a use of their ships, continuing to advocate independent hunting groups, despite the disappointing results these soon proved to have.

Although convoys were introduced in the early part of the war for ships on the short cross-English Channel routes, partly because it was generally assumed that naval escort on a one-to-one ship base was necessary, it was assumed that trans-Atlantic protection would be impossible.

It took the looming U-boat crisis following the entry of the USA into the war in April 1917 to bring about a re-think. With sinkings of merchant ships reaching a level which threatened to force Britain out of the war within months, the Admiralty looked again at the statistics. It was found that most losses fell on ocean-going trade, less than 10% of total shipping, a sufficiently small number to make convoy escorts feasible. The result was a gradual introduction of a convoy system and the construction of growing numbers of dedicated escort vessels to supplement fleet destroyers. Where the convoy was introduced, sinkings were reduced to 1.1% of their previous figure. In the nick of time, the U-boat threat had been countered.

Convoys Revived

The outbreak of war in 1939 found the British Admiralty convinced of the value of the convoy system, though lacking in the resources to adequately re-introduce it. Initially much emphasis was placed on defensive arming of merchant ships, using medium-calibre guns which had for a long time been stockpiled from obsolete warships when they were scrapped. Arming the entire British merchant fleet of 3,000 ocean-going ships and over 1,000 coastal vessels, and training gunners, was an enormous task. 

On 26th August 1939, as war with Germany loomed, the Admiralty assumed control of all British-registered shipping. It exercised control through its Trade Division, and the newly formed Ministry of Shipping, which later became part of the Ministry of War Transport. In order to free up space for war materials, stringent rationing of foodstuffs and other necessities of civilian life was introduced from the outset.

The trade Division was also responsible for the introduction, organisation, and escort of convoys, which began to be used from the outbreak of war. Initially they ran mainly along the British east coast, and as well as coastal trade, included many ocean-going ships moving between ports. These coastal convoys encountered serious problems, mainly because off-shore shoals, and defensive minefields, restricted convoys to narrow coastal channels, where they frequently became strung out and vulnerable to attack by aircraft, mines and German destroyers and high-speed "S" boats.

The Ocean Convoys

For a surprisingly long period after the outbreak of war, many merchant ships, particularly the faster ones, continued to sail independently, and losses to German surface raiders in particular, regarded during the first months of the war as a greater threat than U-boats, were heavy.

Convoys fell into two main categories, The so-called "operational" type were formed for specific missions, such as those run through the Mediterranean for the relief of Malta, and those, typically employing large fast ocean liners, for troop transportation. All of these would normally have a strong naval escort. 

However the type which most concern us here were those run on a regular cycle for the protection of commercial shipping. The coastal type, running up the British East coast between the Thames Estuary and the Firth of Forth in Scotland, were coded FN northwards and FS on their southern journeys. Mainly convoying ships heading to and from the Mediterranean , and running between Britain and Gibraltar, were the HG/OG convoys. Trade from the east coast of South America, and South Africa, the Sl/Os convoys, had Freetown, Sierra Leone, as a rendezvous. 

By far the most important and vital were the North Atlantic convoy routes. Without the safe arrival of the trade they carried, Britain would be unable to continue the war. Until August 1942, when they were shifted to New York, the westward-bound convoys (fast OB, later ON, and slow ONS) terminated at Halifax, Nova Scotia and Cape Breton. The east-bound convoys, starting from these same points, were designated HX (fast) and SC (slow). These speed designations are in some ways deceptive. In theory, a "slow" convoy was one traveling at less than nine knots, but seven knots was generally more common. 

A convoy had two main functions. The first was to count loss rates. It had taken naval experts a long time to realise that far from providing an easier target, a concentration of merchant vessels in a relatively tiny area in fact made them much more difficult for enemy surface and submarine attackers to detect. The second aim was to increase enemy losses, particularly in U-boats, by drawing them into a position where they could be attacked by concentrations of escort vessels, who would thus be much more effective than in frequently fruitless "search and destroy" missions.

The reality was of course for a long time very different from the theory. Although many convoys completed their voyages unscathed and unattacked, the shortage of escort vessels which continued well into the war frequently led to horrendous losses in inadequately protected convoys.

Convoys seldom followed the most direct route to their destinations, but usually followed an evasive course plotted in the hope of avoiding interception. As a result, an Atlantic crossing might be of between 3000 and 5000 miles. A slow convoy might take about 20 days on its voyage, a fast one 15.Sailings were normally at roughly weekly intervals, so that at any one time there might be about half a dozen "loaded" convoys and a similar number of "empty" ones at sea. Given the immensities of ocean involved, the average convoy's chance of avoiding detection was quite good.

Though in relation to the areas of ocean the space occupied by a convoy was miniscule, it did not appear so to the observer. Normally a convoy was formed in a rectangular shape, with a much wider frontage than depth. Ships most commonly occupied nine to eleven parallel columns, each averaging five ships. Both weather conditions and the need to avoid collisions could affect the formation. The distance diagonally across a convoy of 45 ships might be 8000 yards. Escort vessels were about 3000 yards further out in order to stand a chance of detecting U-boats before they came within torpedo range of the merchant ships. Thus the perimeter to be defended might amount in some cases to 60,000 yards, or 30 sea miles.

It is hardly surprising that there were never enough escort vessels available. To demonstrate this, at best an escort's asdic submarine detection system might be effective at 2500 yards. Weather conditions in the Atlantic often halved this. Early sets were often only effective over a very limited arc, so commanders, often with only four escorts available, had great gaps in the their area of coverage, which they could only inadequately attempt to compensate for by constant variations of speed and course.

In action, a convoy's protection would often be weakened still further. If he had detected, or possibly damaged, an attacking U-boat, the instinct of any escort commander was to try to finish off his opponent. But the average corvette had only an 8 knot speed advantage over the merchant ships in its convoy, so if it were absent for two hours searching for or attacking a contact, it might take it a further two hours to catch up with the convoy again. There could thus be a four- hour period when a convoy's protection had been perhaps critically diminished. A further problem for escorts, often with a low endurance, was that the high-speed chase needed to catch up with the convoy would seriously diminish already limited fuel stocks. The earlier corvettes were often coal-fired, so that there was no possibility of re-fuelling at sea.

Further complications for the escort commanders often resulted from convoy losses suffered in enemy attacks. Even if a convoy, as was sometimes the case, was accompanied by a specialised "rescue ship", escorts were often distracted from their primary role by the need to pick up survivors from sinking merchant ships. . Accommodating them in the very limited space aboard an escort was a major problem which seriously impeded the vessel's operational capabilities until the survivors could be transferred to another merchant ship.

At the start of the war, escorts were only provided as far as 12 ½ degrees West, less than 100 miles beyond the west coast of Ireland. Beyond this point vessels would proceed for a time in convoy before splitting up to continue to their destinations. The escort vessels would meanwhile rendezvous with the next east-bound convoy and escort it for the remainder of its voyage. By October 1940, escorts had been extended as far as 19 degrees West.

On the western side of the Atlantic, (prior to the entry into the war of the USA), an increasingly vital role was played by the Royal Canadian Navy. An initially very small number of escort vessels was steadily expanded, mainly by Canadian ship builders. These enabled escorts to be provided as far as 53 ½ degrees West , (just short of the eastern tip of Greenland). This however left a yawning 2000 mile gap in mid Atlantic, where, until about July 1941, no escort could be provided at all, and , where in the early years of the war, no long-range air cover could be provided either.

Escorts and anti-submarine warfare

The U-boat onslaught on Allied merchant shipping in World War I had been a type of warfare unforeseen by naval planners, so that countermeasures were improvised and refined by a process of trial and error. Though by late 1917 the Allies were beginning to get the measure of the U-boat threat, the development of an effective anti-submarine force took time, and, to retain its effectiveness, it would need to be adequately maintained in peacetime.

World War I saw the basic development both of the hydrophone system for detecting submerged submarines, and the increasingly effective use of the depth charge. By the end of the war the hydrophone was being refined and improved into what became known as the "asdic" system, and air power had at least shown its potential value as an anti-submarine weapon.

The post -war period saw continued work by the Royal Navy in improving the effectiveness of "asdic". This basically operated by emitting energy waves into the water which were reflected back when striking a solid object. There were however many factors which could distort or confuse the signals, including water layers of different temperature or salinity, speed and extraneous water noises, sometimes created by the ship using the detection apparatus or others close by. Some of these problems were reduced by improved techniques, including the replacement of hand-cranked asdic apparatus with motor-driven equipment which connected with the ship's gyro repeater, to keep it a constant bearing despite a ship's manoeuvring. Accurate interpretation of asdic signals remained however a skilled and uncertain art.

Anti-submarine warfare techniques received some valuable practical experience during the Spanish Civil War of 1936-9. British warships on neutrality patrols encountered Italian submarines attacking shipping whilst masquerading as Spanish Nationalist vessels. Though no submarines were actually sunk by British vessels, pursuit attempts after attacks, gave practical training in the use, and limitations of, asdic in actual potential combat conditions. Of greater long term significance, the British Admiralty Operational Intelligence Centre which was established, using D/F (directional/finding) stations, made valuable progress in the methods of detecting the handful of German submarines also present in the war zone by means of their signals and other intelligence processes.

A major failure in the development of British anti-submarine warfare in the inter-war years resulted from neglect of naval aviation until the Fleet Air Arm was set up in 1937, and the continued low priority given to the role of air power against submarines. This, and over-confidence in the effectiveness of asdic, would be serious failings in British anti-submarine warfare in 1939.

The outbreak of war found the Royal Navy with 176 destroyers, but of these over 60 dated from World War I. Other naval operations soaked up most of the more modern, faster units, leaving only the older vessels, with limited range and inadequate armament, available for anti-submarine duties. These would be supplemented by armed trawlers and purpose-built corvettes, but it would take some time before these were available in significant numbers. In the early summer of 1940, with the loss of French naval support and Germany's acquisition of France's Atlantic naval bases for her U-boats, Britain was desperately short of escort vessels, with only 74 destroyers available for all needs.

It was in this context that Churchill's appeals to Roosevelt resulted in the transfer to Britain of 50 Us destroyers, mainly of WWI vintage, in return for the granting to the Us of naval bases in the Caribbean. But though the destroyers may have boosted morale, in many cases they proved in need of extensive overhaul, and added little real muscle to the convoy escort force.

For some time there was no real improvement in the capabilities of convoy escorts. The 20 Type I "Hunt" class destroyers, of which much had been hoped, started to be commissioned from early 1941, but they showed themselves quite unsuitable for ocean escort work, and mainly operated in home waters. Almost equally disappointing were the 137 "Flower" class sloop/corvettes, 925 ton vessels which entered service in 1940-1. They proved to be almost useless in winter weather conditions because of uncontrollable rolling and poor manoueverabilty, whilst their top speed of about 15 knots was too slow to catch a surfaced U-boat.

In early 1941 the average convoy of 40-50 ships had only two escorts, far too few to be any real protection. The life of an escort ship crew was a harsh one. Often with only 48 hours snatched rest between voyages, they lived in cramped basic conditions. Watches, often in bitter weather were long and harsh, spent straining to detect signs of a U-boat, whose intended victim they were quite likely to be. Asdic proved particularly unreliable in bad weather, with signals difficult to interpret Long hours were spent straining with night vision binoculars, relieved only by hastily snatched meals of soup or corned beef "sarnies" (sandwiches), and the ubiquitous mug of "kye" (thick cocoa with condensed milk).

Yet gradually the situation improved. May 1941 saw the first convoy to receive "end to end" escort (complete coverage for its entire voyage) . The British and Canadian Navies now had 248 destroyers and destroyer escorts, 99 corvettes and 248 miscellaneous escort vessels, including converted trawlers, sloops etc, raising the average number of escorts per convoy to five. Another 157 destroyers and 99 corvettes were building in Britain and Canada.

In 1943 new escort types, the 1350 ton modified "Black Swan" escort sloops and the 1370 ton "River" class frigates, both with top speeds of 20 knots, began to come into service. Even so, only 50 destroyers and corvettes left British shipyards that year, and 85% of RN escorts came from US construction. However, the average convoy now had eight escorts, and (following on the successful, though brief, career of the first escort carrier, HMS "Audacity" in the autumn off 1941, the first "support" groups, dedicated U-boat hunting task groups, some with escort carriers attached, began at last to turn the tide of the Battle of the Atlantic.

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Copyright © 2002 John Barratt.

Written by John Barratt. If you have questions or comments on this article, please contact John Barratt at:
johnbarratt46@johnbarratt46.plus.com.

About the author:
John Barratt has authored many books to include: Armada 1588,  The Battle of Marston Moor, The Civil War in South-West England 1642-1646, and Cavalier Generals.

Published online: 12/15/2002.
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