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A convoy is a group of , typically motor vehicles or ships, traveling together for mutual support and protection. Often, a convoy is organized with armed defensive support and can help maintain cohesion within a unit. It may also be used in a non-military sense, for example when driving through remote areas.
By the French Revolutionary Wars of the late 18th century, effective naval warfare convoy naval tactics had been developed to ward off and . 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 as hard to find as a single ship. Even if the privateer found a convoy and the wind was favourable for an attack, it could still hope to capture only a handful of ships before the rest managed to escape, and a small escort of warships could easily thwart it. As a result of the convoy system's effectiveness, wartime insurance premiums were consistently lower for ships that sailed in convoys.
Many naval battles in the Age of Sail were fought around convoys, including:
By the end of the Napoleonic Wars, the Royal Navy had in place a sophisticated convoy system to protect merchant ships. Losses of ships travelling out of convoy, however, were so high that no merchant ship was allowed to sail unescorted.
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 the German capital ships had been bottled up in the North Sea, and the main threat to shipping came from . From a tactical point of view, World War I–era were similar to privateers in the age of sail. These submarines were 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 in April 1917 convoys were trialled, before being officially introduced in the Atlantic in September 1917. Other arguments against convoys 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 an escort. 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.
In his book On the Psychology of Military Incompetence, Norman Dixon suggested that the hostility towards convoys in the naval establishment were in part caused by a (sub-conscious) perception of convoys as effeminating, due to warships having to care for civilian merchant ships.Dixon, Dr. Norman F. On the Psychology of Military Incompetence Jonathan Cape Ltd 1976 / Pimlico 1994 pp. 210–211 Convoy duty also exposes the escorting warships to the sometimes hazardous conditions of the North Atlantic, with only rare occurrences of visible achievement (i.e. fending off a submarine assault).
The capability of a heavily armed warship against a convoy was dramatically illustrated by the fate of Convoy HX 84. On November 5, 1940, the German heavy cruiser encountered the convoy. Maiden, Trewellard, and Kenbame Head were quickly sunk, with Beaverford and Fresno City suffering the same fate later. Only the sacrifices of the armed merchant cruiser and the freighter Beaverford to stall the Scheer, in addition to failing light, allowed the rest of the convoy to escape.
The deterrence value of a battleship in protecting a convoy was also dramatically illustrated when the German light battleships (referred by some as battlecruisers) and , mounting guns, came upon an eastbound British convoy (HX 106, with 41 ships) in the North Atlantic on February 8, 1941. When the Germans detected the slow but well-protected battleship escorting the convoy, they fled the scene rather than risk damage from her 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.
Prior to overt participation in World War II, the US was actively engaged in convoys with the British in the North Atlantic Ocean, primarily supporting British activities in Iceland.
After Germany declared war on the US, the US Navy decided not to organize convoys on the American eastern seaboard. US 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.
Several notable battles in the South Pacific involved Allied bombers interdicting Japanese troopship convoys which were often defended by Japanese fighters, notable Guadalcanal (13 November 1942), Rabaul (5 January 1943), and the Battle of the Bismarck Sea (2–4 March 1943).
At the Battle off Samar, the effectiveness of the U.S. Navy's escorts was demonstrated when they managed to defend their troop convoy from a much larger and more powerful Japanese battle-fleet. The Japanese force comprised four battleships and numerous heavy cruisers, while the U.S. force consisted of escort carriers, destroyers, and destroyer escorts. Large numbers of American aircraft (albeit without much anti-ship ordnance other than torpedoes) and aggressive tactics of the destroyers (with their radar-directed gunfire) allowed the U.S. to sink three Japanese heavy cruisers at the cost of one escort carrier and three destroyers.
The Allied responses included:
They were also aided by
The convoy prefix indicates the route of the convoy. For example, 'PQ' would be Iceland to Northern Russia and 'QP' the return route.
In practice, Type VII and Type IX U-boats were limited in their capabilities. Submerged speed and endurance was limited and not suited for overhauling many ships. Even a surfaced U-boat could take several hours to gain an attack position. Torpedo capacity was also restricted to around fourteen (Type VII) or 24 (Type IX), thus limiting the number of attacks that could be made, particularly when multiple firings were necessary for a single target. There was a real problem for the U-boats and their adversaries in finding each other; with a tiny proportion of the ocean in sight, without intelligence or radar, warships and even aircraft would be fortunate in coming across a submarine. The Royal Navy and later the United States Navy each took time to learn this lesson. Conversely, a U-boat's radius of vision was even smaller and had to be supplemented by regular long-range reconnaissance flights.
For both major allied navies, it had been difficult to grasp that, however large a convoy, its "footprint" (the area within which it could be spotted) was far smaller than if the individual ships had traveled independently. In other words, a submarine had less chance of finding a single convoy than if it were scattered as single ships. Moreover, once an attack had been made, the submarine would need to regain an attack position on the convoy. If, however, an attack were thwarted by escorts, even if the submarine had escaped damage, it would have to remain submerged for its own safety and might only recover its position after many hours' hard work. U-boats patrolling areas with constant and predictable flows of sea traffic, such as the United States Atlantic coast in early 1942, could dismiss a missed opportunity in the certain knowledge that another would soon present itself.
The destruction of submarines required their discovery, an improbable occurrence on aggressive patrols, by chance alone. Convoys, however, presented irresistible targets and could not be ignored. For this reason, the U-boats presented themselves as targets to the escorts with increasing possibility of destruction. In this way, the Ubootwaffe suffered severe losses, for little gain, when pressing pack attacks on well-defended convoys.
In the present day, convoys are used as a tactic by navies to deter pirates off the coast of Somalia from capturing unarmed civilian freighters who would otherwise pose easy targets if they sailed alone.
In the 1990s these convoys became common traveling from Western Europe to countries of the former Yugoslavia, in particular Bosnia and Kosovo, to deal with the aftermath of the wars there. They also travel to countries where standards of care in institutions such as orphanages are considered low by Western European standards, such as Romania; and where other disasters have led to problems, such as around the Chernobyl disaster in Belarus and Ukraine.
The convoys are made possible partly by the relatively small geographic distances between the stable and affluent countries of Western Europe, and the areas of need in Eastern Europe and, in a few cases, North Africa and even Iraq. They are often justified because although less directly cost-effective than mass freight transport, they emphasise the support of large numbers of small groups, and are quite distinct from multinational organisations such as United Nations humanitarian efforts.
Truckers' convoys were created as a byproduct of the U.S.' national 55 mph speed limit and 18-wheelers becoming the prime targets of . Most truckers had difficult schedules to keep and as a result had to maintain a speed above the posted speed limit to reach their destinations on time. Convoys were started so that multiple trucks could run together at a high speed with the rationale being that if they passed a speed trap the police would only be able to pull over one of the trucks in the convoy. When driving on a highway, convoys are also useful to conserve fuel by drafting.
The film Convoy, inspired by a 1975 song of the same name, explores the camaraderie between , where the culture of the CB radio encourages truck drivers to travel in convoys.
Truck convoys are sometimes organized for fundraising, charity, or promotional purposes. They can also be used as a form of protest, such as the Canada convoy protest in 2022.
During the Cold War with its high number of military exercises, the military was the main user of convoy rights. Today, catastrophes like large-scale flooding might bring a high number of flagged convoys to the roads. Large-scale evacuations for the disarming of World War II bombs are another common reason for non-governmental organization (NGO) unit movements under convoy rights.
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