A convoy is a group of vehicles (of any type, but usually motor vehicles or ships) traveling together for mutual support. Often, a convoy is organized with armed defensive support, though it may also be used in a non-military sense, for example when driving through remote areas. If one vehicle breaks down or gets stuck, the other vehicles can assist with repairs or attempt to free the bogged-down vehicle. If repairs are not possible, the people from the broken-down vehicle can transfer to others.
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.
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 in April 1917 convoy was trialled, before being officially introduced in the Atlantic in September 1917.
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.
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. Also, it should be noted that convoy duty exposes the escorting warships to the uncomfortable and sometimes outright hazardous conditions of the North Atlantic, but with only extremely rare occurrences of visible achievement (i.e. fending off a submarine assault).
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 warships 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:
The Allied responses included:
They were also aided by
Many naval battles of World War II were fought around convoys, including:
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 travelled 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.
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 defendera.
In the 1990s these convoys became common travelling 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.
Trucker convoys were created as a byproduct of the 55mph speed limit and 18-wheelers becoming the prime targets of speed traps. Most truckers had difficult schedules to keep and as a result had to maintain a speed above the posted speed limit in order to reach their destinations on time. Convoys were started so that multiple trucks could run together at a high speed with the thinking being that if they passed a speed trap the police would only be able to pull over one of the trucks in the convoy.