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.
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
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
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
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.
Copyright © 2002 John Barratt.
Written by John Barratt. If you have questions or comments on this article,
please contact John Barratt at:
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.