TheFrenchruse de guerre, sometimes literally translated asruse of war, is a non-uniform term; generally what is understood by "ruse of war" can be separated into two groups. The first classifies the phrase purely as an act ofmilitary deception against one's opponent; the second emphasizes acts against one's opponent by creative, clever, unorthodox means, sometimes involving force multipliers or superior knowledge.^[1] The termstratagem, fromAncient Greekstrategema (στρατήγημα, 'act of generalship'), is also used in this sense.

Ruses de guerre are described from ancient to modern times, both in semi-mythical accounts such as the story of theTrojan Horse inVirgil'sAeneid, and in well-documented events such as the flying of the American flag by the British ocean linerRMSLusitania in 1915 (whilst the United States was aneutral country) to deter attack by German submarines; they also feature in fiction.

The termruse de guerre is given legal meaning within therules of war. Good faith is required, but at least 17 different types ofruse, includingambushes, false radio messages, the use of spies and the use of dummy guns, are considered legitimate as long as they do not involve treachery orperfidy.Landmines and similar traps can be considered perfidious under the rules in certain circumstances. Explicitly prohibitedruses under article 23 of theHague Convention of 1907 include improper use of aflag of truce or the military insignia of the enemy.

According toHomer's somewhatmythical account in theIliad, the Greeks during theTrojan War pretended to give up their fruitless ten-year siege of the city ofTroy and sailed away, leaving behind theTrojan Horse. After the Trojans pulled what they believed was a parting gift within the walls of the city, soldiers that had hidden inside the hollow horse during the previous night emerged and opened the city's gates, allowing the awaiting army to enter the city.

Prior to a naval battle with KingEumenes II ofPergamon,Hannibal sent a herald with a message for the opposing commander. That was a trick aiming to locate Eumenes's ship so that Hannibal could concentrate his forces against it.^[2]

Alexander the Great walked his men up and down a river continuously to condition his opponent,Porus, into a false sense of security in the belief that his whole army was searching for a ford. Then, under the cover of night Alexander marched a contingent of his men upriver and crossed the Indus, while his remaining forces marched south to their camp as they usually did. This feint allowed Alexander to hide his troops' location and win theBattle of Hydaspes in 326 BC.

As stated in the probably fictional account inRomance of the Three Kingdoms,Zhuge Liang trickedSima Yi using theEmpty Fort Strategy fromSun Tzu'sThe Art of War. Zhuge Liang sat upon the walls of the cities, his men far outnumbered by the Wei army which was advancing toward him. Zhuge Liang sat upon the walls and played his instrument, seemingly calm and composed, tricking Sima Yi into thinking that the Shu troops had hidden in the surrounding area for an ambush. Zhuge Liang was able to quickly flee the area as the Wei retreated.

TheSiege of Detroit was an early engagement in theWar of 1812, where a smaller British-First Nations force, led by Major-GeneralIsaac Brock andShawnee leaderTecumseh, used bluff and deception to intimidate Brigadier GeneralWilliam Hull into surrendering thefort, the town ofDetroit, and a dispirited American force that nevertheless outnumbered the British and First Nations. Intercepting American dispatches from Fort Detroit, Brock judged the morale of the American garrison to be low, and that the American general had a fear of First Nations in particular. Brock arranged for misleading letters to fall into American hands, stating an inflated figure of 5,000 First Nations warriors were already inAmherstburg, to simulate a larger First Nations force had attached themselves to his army.^[3] Prior to the siege, Brock also sent a letter demanding for surrender to Hull, stating:

The force at my disposal authorizes me to require the immediate surrender of Detroit. It is far from my intention to join in a war of extermination, but you must be aware, that the numerous body of Indians who have attached themselves to my troops, will be beyond my control the moment the contest commences.

— Major-GeneralIssac Brock^[3]

To further the illusion that a large First Nations force was attached with Brock's force, Tecumseh extended his men, and marched them three times through an opening in the woods at the rear of the fort in full view of the fort.^[4] Brock similarly dressed members of theCanadian militia as British regulars, and instructed soldiers to light individual fires instead of one fire per unit, thereby creating the illusion of a much larger army.^[3]

Use of deception to mask an inferior force was also used in another battle during the War of 1812, theBattle of Chateauguay. Outnumbered during battle, theCanadian Fencibles were initially outflanked and falling back, before Lieutenant-ColonelCharles de Salaberry of theCanadian Voltigeurs orderedbugle calls, cheers and Indian war whoops, in a ruse to make the Americans believe that they were about to be enveloped. Fearing themselves outnumbered and about to be outflanked, Brigadier-GeneralWade Hampton called off the American advance, withdrawing his forces toPlattsburgh, New York.^[5][6]

During theAmerican Civil War,Union GeneralGeorge Meade's General Order No. 13 of 1865 was retracted after it was determined that his criticism of Brigadier-General McLaughlin was based on "nothing more than the obvious result of thoseruses de guerre, by which the very best officers may, at times, be victimized", after theConfederate Army falsely claimed that it had gained a foothold in theUnion Army lines.^[7]

An effort by theImperial Japanese Navy to lure the Russian fleet out of its harbor during theRusso-Japanese War in 1904 was described byThe New York Times as "a clever ruse of war to entice the Russian ships out ofPort Arthur".^[8]

The use of the American flag flown on thelinerLusitania while crossing through theIrish Sea to avoid attack by German submarines during theFirst World War was criticized in debate in theUnited States House of Representatives byRepublicanEben Martin ofSouth Dakota, who stated that "the United States cannot be made a party to a ruse of war where the national colors are involved".^[9]

During theSecond World War, the crew of the merchant-raiding German light cruiserEmden rigged a dummy fourthfunnel on top of her radio room to disguise her as a British cruiser, most of which were equipped with four funnels. During First and Second World Wars,Q-ships were heavily armed merchant ships with concealed weaponry, designed to lure submarines into making surface attacks. This gave Q-ships the chance to open fire and sink them.

During theSecond Sino-Japanese War, the former Imperial Japanese Navy battleshipAsahi, which had been taken out of reserve shortly after the outbreak of war for use as a troop transport but then converted to a repair ship, was fitted with dummy woodenmain batteries fore and aft to resemble an old battleship after her arrival inShanghai on 29 December 1938.

In the lead up to theFirst Battle of Sirte during the Second World War, the fast minelayerHMS Abdiel successfully impersonated a force of two battleships using false signals traffic, as part of a decoy mission against Italian forces.

The AlliedCombined Operationsraid on theNormandie Dock inSaint Nazaire employed several legitimate ruses during their voyage up theLoire estuary, including flying German colours and replying to signal challenges by giving misleading replies in German. These measures were all designed to buy time for the attacking force. When these tactics ceased to be effective and German shore batteries opened fire in earnest, all the British ships lowered their German colours and hoistedWhite Ensigns before returning fire.

GermancommandoOtto Skorzeny led his troops wearing American uniforms to infiltrate American lines inOperation Greif during theBattle of the Bulge. Skorzeny later reported that he was told by experts in military law that wearing American uniforms was a defensibleruse de guerre, provided his troops took off their American uniforms, and put on German uniforms, prior to firing their weapons. Skorzeny was acquitted by a United States military court inDachau in 1947, after his defense counsel argued that the "wearing of American uniforms was a legitimate ruse of war forespionage andsabotage" as described byThe New York Times.^[10]

According to the rules of war, good faith in dealing with the enemy must be observed as a rule of conduct, but this does not prevent measures such as usingspies andsecret agents, encouragingdefection orinsurrection among the enemycivilian population, corrupting enemy civilians or soldiers by bribes, or inducing the enemy's soldiers todesert,surrender, orrebel. In general, a belligerent may resort to those measures for mystifying or misleading the enemy against which the enemy ought to take measures to protect itself.^[11]

Legitimate ruses include:^[11]

• surprises;ambushes; feigned attacks,retreats, or flights;
• simulating quiet and inactivity (to lull the enemy into complacency);
• use of small forces to simulate large units (for example, inducing an enemy unit to surrender by pretending that it is surrounded by a large force);
• transmitting false or misleadingradio ortelephone messages;
• deception of the enemy by bogus orders purporting to have been issued by the enemy commander;
• making use of the enemy's signals andpasswords or secret handshakes;
• pretending to communicate with nonexistent troops or reinforcements;
• deceptive supply movements (which might make the enemy think you are preparing for action when you're not);
• deliberate planting of false information;
• use of spies and secret agents;
• moving landmarks (to confuse the enemy operating in unfamiliar territory);
• putting up dummy guns and vehicles or laying dummy mines;
• erection of dummy installations and airfields (to intimidate or encourage useless attack);
• removing unit identifications (but not those that identify the belligerent while in combat) fromuniforms;
• psychological warfare activities;
• disguising awarship to appear to be a neutralmerchant vessel, or a merchant vessel on the side of one's opponent, has traditionally been considered a legitimateruse de guerre, provided the belligerent raises their own flag to break the deception before firing their guns. This was calledsailing underfalse colors. Both sides during the world wars used this tactic, most famously the Royal Navy'sQ ships. The German raiderKormoran used this tactic against the superiorHMAS Sydney, disguising herself as theDutch merchant vesselStraat Malakka prior to their mutually destructiveengagement.
• disguising a warship to appear to be one of the warships of one's opponent has traditionally been considered to be a legitimateruse de guerre, provided the belligerent raises their own flag to drop the disguise, prior to firing their guns. The Germans took steps to disguise theirpocket battleships asAllied cruisers during the Second World War. This tactic was also used by theRoyal Navy to great effect during theNapoleonic Wars, since the boarding and capture of enemy vessels was quite common during that time, and information about the current ownership of vessels was not easy to disseminate rapidly.

Further, according to the rules of war, ruses of war are legitimate so long as they do not involveperfidy on the part of the belligerent resorting to them. They are, however, forbidden if they contravene any generally accepted rule.^[11][12]

• traps that are attached or associated in any way with:
  • sick, wounded, or dead;
  • burial, cremation, or graves;

Article 23 of the1907 Hague ConventionIV – The Laws and Customs of War on Land provides that: "It is especially forbidden....(b) To kill or wound treacherously individuals belonging to the hostile nation or army....(f) To make improper use of aflag of truce, of thenational flag, or of the military insignia andmilitary uniform of the enemy, as well as the distinctive badges of theGeneva Convention".^[13]Protocol I of the Geneva Conventions expanded the rules of prohibiting certain type of ruses as defined in Articles 37, 38, and 39.

The line of demarcation between legitimate ruses and forbidden acts of perfidy is sometimes indistinct. In general, it would be an improper practice to secure an advantage over the enemy by deliberate lying or misleading conduct which involves abreach of faith, or when there is amoral obligation to speak thetruth. For example, it is improper to pretend tosurrender to secure an advantage over the opposing belligerent.^[14]

To broadcast to the enemy that anarmistice had been agreed upon when such is not the case would be treacherous.^[15] Abuse of the protections afforded to medical personnel (by disguising combat soldiers as medics, or by putting ared cross on a combat vehicle) is also considered unacceptable. In August 1946, a German soldier, Heinz Hagendorf, was found guilty by a U.S.military tribunal at theDachau Trials and sentenced to six months imprisonment for having "wrongfully used theRed Cross emblem in a combat zone by firing a weapon at American soldiers from an enemy ambulance displaying such emblem." The verdict and sentence were upheld on appeal.^[16]

• Stratagems (Latin:Strategemata), by the 1st-century Roman authorFrontinus, which concerns military stratagems drawn from Greek and Roman history.
• Stratagems (Ancient Greek:Στρατήγηματα), book by the 2nd-century Macedonian authorPolyaenus which concerns military strategems. In common with Frontinus' work (see above), the title is sometimes given asStrategemata.
• Stratagems of the Warring States, English title of a Chinese book compiled between the 3rd to 1st centuriesBCE. Alternative English titles includeStrategies of the Warring States.
• Thirty-Six Stratagems, English title of a Chinese book concerning stratagems which have military and civil applications.