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Commerce raiding is a form of naval warfare used to destroy or disrupt logistics of the enemy on the open sea by attacking its merchant shipping, rather than engaging its combatants or enforcing a blockade against them. It is also known, in French, as guerre de course (literally, "war of the chase") and, in German, Handelskrieg ("trade war"), from the nations most heavily committed to it historically as a strategy.
Commerce raiding was heavily criticised by the naval theorist A.T. Mahan, who regarded it as a distraction from the destruction of the enemy's fighting power. Nevertheless, commerce raiding was an important part of naval strategy from the Early Modern period through the Second World War.
Usually, commerce raiding is chosen by a weaker naval power against a stronger, or by a nation with little ocean-going trade against one with a great deal. The best protection against a commerce raiding strategy is for merchant vessels to sail in convoy, protected by naval escorts.
The first sort of commerce raiding was for nations to commission privateers. Early instances of this type of warfare were by the British and Dutch against the Spanish treasure fleets of the 16th century, which resulted in financial gain for both captain and crew upon capture of enemy vessels ("prizes").
This quickly became a major commercial enterprise, with privateer vessels, often in groups, being outfitted by venture capital, with investors also sharing in the returns. The practice rapidly spread. A privateer was distinguished from a pirate by the letter of marque, by which the vessel was commissioned as a private man-of-war. Captured vessels and cargo were submitted, in Britain's case, to Admiralty courts, where they might be condemned for sale, or, if the captures were not found to be within the rules of war, they might be released, sometimes with awards for damages.
Privateers formed a large part of the total military force at sea during the 17th and 18th centuries. In the First Anglo-Dutch War, English privateers attacked the trade on which the United Provinces entirely depended, capturing over 1,000 Dutch merchant ships. During the subsequent war with Spain, Spanish and Flemish privateers in the service of the Spanish Crown, including the notorious Dunkirkers, captured 1,500 English merchant ships, helping to restore Dutch international trade. Dutch privateers and others also attacked British trade, whether coastal, Atlantic, or Mediterranean, in the Second and Third Anglo-Dutch wars.
During the Nine Years War, French policy strongly encouraged privateers, including the famous Jean Bart, to attack English and Dutch shipping. England lost roughly 4,000 merchant ships during the war. In the following War of Spanish Succession, privateer attacks continued, Britain losing 3,250 merchant ships. Parliament passed an updated Cruisers and Convoys Act in 1708, allocating regular warships to the defence of trade.
In the War of Austrian Succession, the Royal Navy was able to concentrate more on defending British ships. Britain lost 3,238 merchantmen, a smaller fraction of her merchant marine than the enemy losses of 3,434. While French losses were proportionally severe, the smaller but better-protected Spanish trade suffered the least, and Spanish privateers enjoyed much of the best allied plunder of British trade, particularly in the West Indies.
During Britain's wars against revolutionary and Napoleonic France, the Royal Navy dominated the seas. France adopted a guerre de course strategy by licensing civilian privateers to seize British shipping. British East Indiamen of the time were therefore heavily armed to protect themselves against such raids, at the cost of considerable speed and maneuverability. Some East Indiamen, such as the Arniston, were successfully able to fend off these attacks in other parts of the world; others, such as when Kent met Confiance in 1800, were less fortunate.
During the American Civil War, the Confederate Navy operated a fleet of commissioned Confederate States Navy commerce raiders. These differed from privateers as they were state-owned ships with orders to destroy enemy commerce rather than privately owned ships with letters of marque. These included Sumter, Florida, Alabama, and Shenandoah. Most of the ships used in this period were built in Britain, which resulted in the Alabama Claims.
By the 1880s, the navies of Europe began to deploy warships made of iron and steel. The natural evolution that followed was the installation of more powerful guns to penetrate the new steel warships. No longer would navies fight for "prizes", in which capture of the enemy warship meant financial gain for captain and crew as well as government when the prize and her cargo were auctioned. The advent of steel armor and high explosive and armor-piercing shells meant the destruction and sinking of enemy "men o' war" was the priority. First seen at the Sinope in 1853, the change was little appreciated until 1905, when at Tsushima seven pre-dreadnoughts were sent to the bottom, and the only prizes were those that had voluntarily surrendered.
World War I saw Germany conducting a commerce war ("Handelskrieg") against Britain and her allies, principally with U-boats, but also with merchant raiders and light cruisers, and even occasionally with naval airships.
During World War II, the Battle of the Atlantic saw Nazi Germany conducting guerre de course against Britain and its allies, again using U-Boats, auxiliary cruisers, and small groups of cruisers and battleships (raiders).
Limitations set by the Treaty of Versailles meant Germany could not build a large battle fleet as she had in the time leading up to the World War I, and chose to covertly develop her submarines instead. U-boats were cheaper and quicker to build than capital ships, and consequently Germany built up a submarine force rather than a surface fleet. This meant Germany was not able to fight a war of "guerre d'escadre" (battles between fleets), and therefore pursued guerre de course; what small numbers of surface warships Germany possessed, such as the Deutschlands, as well as her auxiliary cruisers, also participated in this strategy. In addition, a number of commercial vessels were converted, perhaps the most famous being Atlantis.
During World War II, elements of the United States Navy based in Brazil conducted operations in the Atlantic against German commerce raiders and blockade runners. In the Pacific, the U.S. Navy operated against Japanese merchant shipping, as well as engaging in offensive operations against ships of the Japanese Imperial Navy. The bulk of the Japanese merchant marine was sunk by American submarines. By the end of the war, only 12% of Japan's pre-war merchant tonnage was still afloat.
The Indian Ocean raid was a naval sortie by the Carrier Striking Task Force of the Japanese Navy from 31 March to 10 April 1942 against Allied shipping and bases in the Indian Ocean. It was an early engagement of the Pacific campaign of World War II.
The staff of the Imperial Japanese Navy decided to send some raiders to Indian Ocean waters during December 12, 1941 – July 12, 1942. The Germans had already been operating in the area and conducted mutual aid with Japanese submarines, in the form of re-supply and military intelligence. The Indian Ocean was the largest operating area involving direct contact between the two Axis partners, in which their primary objective was to keep pressure on the shipping lanes. The Japanese Navy participated in some commerce raiding, but concentrated its efforts toward a "decisive battle" in the Pacific, which never took place.