Convoy

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Convoy

A convoy is a group of vehicles or ships traveling together for mutual support. Often, a convoy is organized with armed defensive support. In effect, it is a modification of a caravan.

For example, driving by car through a desert is safer in a convoy. If one vehicle breaks down, the passengers from the others can help with repairs. If repairs are not possible, the people from the broken-down car can transfer to others.

Naval convoys

Age of Sail

By the French Revolutionary Wars of the late 18th century, effective naval convoy tactics had been developed to ward off pirates and privateers. Some convoys contained several hundred merchant ships. The most enduring system of convoys were the Spanish treasure fleets, that sailed from the 1520s until 1790.

When merchant ships sailed independently, a privateer could cruise a shipping lane and capture ships as they passed. Ships sailing in convoy presented a much smaller target: a convoy was no more likely to be found than a single ship. Even if the privateer found a convoy and the wind was favourable for an attack, it could hope to capture only a handful of ships before the rest managed to escape, and a small escort of warships could easily thwart it.

Many naval battles in the age of sail were fought around convoys, including:

World War I

In the late 19th century, the dreadnought changed the balance of power in convoy battles. Steaming faster than merchant ships and firing at long ranges, a single battleship could destroy many ships in a convoy before the others could scatter over the horizon. To protect a convoy against a capital ship required providing it with an escort of another capital ship, a very high cost.

Battleships were the main reason that the British Admiralty did not adopt convoy tactics at the start of the first Battle of the Atlantic in World War I. But by the end of 1914, German capital ships had largely been cleared from the oceans and the main threat to shipping came from U-boats. From a tactical point of view, World War I-era submarines were similar to privateers in the age of sail: only a little faster than the merchant ships they were attacking, and capable of sinking only a small number of vessels in a convoy because of their limited supply of torpedoes and shells. The Admiralty took a long time to respond to this change in the tactical position, and only in 1917, at the urging of the British Prime Minister, David Lloyd George, did they institute a convoy system. Losses to U-boats dropped to a small fraction of their former level.

Other arguments against convoy were raised. The primary issue was the loss of productivity, as merchant shipping in convoy has to travel at the speed of the slowest vessel in the convoy and spent a considerable amount of time in ports waiting for the next convoy to depart. Further, large convoys were thought to overload port resources.

Actual analysis of shipping losses in World War I disproved all these arguments, at least so far as they applied to transatlantic and other long-distance traffic. Ships sailing in convoys were far less likely to be sunk, even when not provided with any escort at all. The loss of productivity due to convoy delays was small compared with the loss of productivity due to ships being sunk. Ports could deal more easily with convoys because they tended to arrive on schedule and so loading and unloading could be planned.

World War II

The British adopted a convoy system the moment that World War II was declared. Canadian, and later American, supplies were vital for Britain to continue its war effort. The course of the second Battle of the Atlantic was a long struggle as the Germans developed anti-convoy tactics and the British developed counter-tactics to thwart the Germans.

The power of a battleship against a convoy was dramatically illustrated by the fate of Convoy HX-84. On November 5, 1940, the German pocket battleship Admiral Scheer encountered the convoy. Maiden, Trewellard, Kenbame Head, Beaverford, and Fresno were quickly sunk, and other ships were damaged. Only the sacrifice of the Armed Merchant Cruiser HMS Jervis Bay and failing light allowed the rest of the convoy to escape.

The power of a battleship in protecting a convoy was also dramatically illustrated when the German battlecruisers Scharnhorst and Gneisenau came upon an eastbound British convoy of 41 ships, HX 106 in the North Atlantic on February 8th, 1941. When they noticed the presence in the escort of the old battleship, HMS Ramillies, they fled the scene, rather than risk damage from her 15" guns.

The enormous number of vessels involved and the frequency of engagements meant that statistical techniques could be applied to evaluate tactics: an early use of operational research in war.

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. 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.

The German anti-convoy tactics included:

long-range surveillance aircraft to find convoys;
strings of U-boats (wolf packs) that could be directed onto a convoy by radio;
breaking the British naval codes;
improved anti-ship weapons, including magnetic and sonic homing torpedoes.

The Allied responses included:

air raids on the U-boat bases at Brest and La Rochelle;
converted merchant ships, eg, Merchant aircraft carriers, Catapult Aircraft Merchantman and armed merchant cruisers
more convoy escorts, including cheaply produced corvettes, frigates, and escort carriers;
improved anti-submarine weapons such as the hedgehog;
long-range aircraft patrols to find U-boats;
larger convoys, allowing more escorts per convoy as well as the extraction of enough escorts to form support groups that operated in defence of convoys that faced an above-average risk of attack
allocating vessels to convoys according to speed, so that faster ships were less exposed.

They were also aided by

improved sonar (ASDIC) allowing escort vessels to better track U-boats;
breaking the German naval cipher;
improved radar and radio direction finding allowing planes to find and destroy U-boats;

During World War II, Japanese vessels rarely traveled in convoys (see also USS Grayback (SS-208) and USS Thresher (SS-200)). Their merchant fleet was largely destroyed by Allied submarines.

Many naval battles of World War II were fought around convoys, including:

Convoy PQ-16, May 1942
Convoy PQ-17, June-July 1942
Operation Pedestal, August 1942
The Naval Battle of Guadalcanal, November 1942
The Battle of the Barents Sea, December 1942
The Battle of the Bismarck Sea, March 1943

The convoy prefix indicates the route of the convoy. For example, 'PQ' would be Iceland to Northern Russia and 'QP' the return route.

Post-WWII

The largest convoy effort since World War II was Operation Earnest Will, the U.S. Navy's 1987–88 escort of reflagged Kuwaiti tankers in the Persian Gulf during the Iran-Iraq War.

It seems that satellite surveillance, aircraft carriers, cruise missiles and modern submarines have turned the tactical advantage decidedly in favour of the attacker. See the modern naval tactics article for an idea of the problems facing the defender.

External links

Naval warfare | Transportation