Convoy A convoy is a group of vehicles , typically motor vehicles or ships , traveling together for mutual support and protection . 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 . Naval convoys . Age of sail . Naval convoys have been used for years , and examples of merchant ships traveling under naval protection have been traced back to the 12th century . The use of organized naval convoys dates from when ships began to be separated into specialist classes and national navies were established . By the French Revolutionary Wars of the late 18th century , effective naval convoy tactics had been developed to ward off pirates and privateer s . Some convoys contained several hundred merchant ships . The most enduring system of convoys were the Spanish treasure fleet s , 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 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 traveling out of convoy were so high that no merchant ship was allowed to sail unescorted . World War I . In the early 20th 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 , at 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 the German capital ships had been bottled up in the North Sea , and the main threat to shipping came from U - boat s . From a tactical point of view , World War I – era submarine s 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 . 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 ) . World War II . The British adopted a convoy system , initially voluntary and later compulsory for almost all merchant ships , the moment that World War II was declared . Each convoy consisted of between 30 and 70 mostly unarmed merchant ships . 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 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 " , " Kenbame Head " , " Beaverford " , and " Fresno " were quickly sunk , and other ships were damaged . Only the sacrifice of the Armed Merchant Cruiser 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 battleships and , carrying 11 " guns , came upon an eastbound British convoy of 41 ships , HX - 106 in the North Atlantic on February 8 , 1941 . When they noticed the presence in the escort of the old battleship , 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 . Prior to overt participation in WWII , the US was actively engaged in convoys with the British in the North Atlantic Ocean , primarily supporting British activities in Iceland . This was discussed by John T . Flynn in his 1944 work " The Truth About Pearl Harbor " 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 . The German anti - convoy tactics included : The Allied responses included : They were also aided by During World War II , Japan ese vessels rarely traveled in convoys . As a result , their merchant fleet was largely destroyed by Allied submarines . 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 . Analysis . The success of convoys as an anti - submarine tactic during the world wars can be ascribed to several reasons related to u - boat capabilities , the size of the ocean and convoy escorts . In practice , Type VII and Type IX U - boat s 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 . Post - World War II . 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 . 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 . Humanitarian aid convoys . The word " convoy " is also associated with groups of road vehicles being driven , mostly by volunteers , to deliver humanitarian aid , supplies , and — a stated objective in some cases — " solidarity " . 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 . The film " Convoy " , inspired by a 1975 song of the same name , explores the camaraderie between truck driver s , where the culture of the CB radio encourages truck drivers to travel in convoys . Truckers ' convoys were created as a byproduct of the 55 mph 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 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 . When driving on a highway , convoys are also useful to conserve fuel by drafting . The truckers ' convoy is more similar to a caravan than a military convoy .