“All warfare is based on deception. Hence, when we are able to attack, we must seem unable; when using our forces, we must appear inactive; when we are near, we must make the enemy believe we are far away; when far away, we must make him believe we are near.” ― Sun tzu, The Art of War
Kant
Telling the truth, according to Immanuel Kant, is a duty that must be the basis of all duties. If exceptions were admitted or allowed, then the performance of such laws would be rendered uncertain and ineffectual. His prohibition against lying is absolute.
How then would Kant conduct a war, a domain of social phenomena based on deception, if he were a soldier on the battlefield? Will a Kant with a gun risk his life for the sake of the philosophical position against lying?
Or, is there an acceptable form of lying and deception in Kantian version of jus ad bello (ethics for combatants)?
Hague and Geneva Conventions
Kant may or may not have an exception for war but Hague and Geneva Conventions do certainly permit deception and misinformation to an extent.
“Ruses of war and the employment of measures necessary for obtaining information about the enemy and the country are considered permissible." — Hague Convention of 1907
The Geneva Convention, too, does not prohibit misinformation, decoy, and mock operations.
However, there are certain deceptions that are prohibited even in war. For example, one can't kill by misusing the red cross symbol or such other insignia or badges whose misuse will destroy the "good faith," which holds life together universally.
Breach of Good Faith: An Example
Emer de Vattel wrote in 1758 about an incident that happened between an English frigate and some French sailors. He's reacting to a report that an English frigate approached the coast of France at the beginning of a conflict between England and France. The English frigate then sent out distress signals and successfully drew out some vessel. They then seized the sailors who responded to their distress signal and made prisoners of them. "If the report be true," de Vattel says, "the contemptible trick deserves severe punishment".
The Harm From Breach of Good Faith
Emer de Vattel then goes on to argue that deception of this nature tends to discourage charitable assistance, a sacred duty among men and a commendable job between enemies.
Message Implied By Distress Signal
Emer de Vattel concluded by saying that asking for help, by sending out a distress signal, is to impliedly promise safety to those who give help. So the action attributed to the English frigate was a detestable breach of good faith.
Yamashita standard
Tomoyuki Yamashita, a Japanese General, was tried for the ugly things done by the Japanese troops in the Philippines, in 1944, under his command. He was found guilty by the court and sentenced to death by hanging in 1946 although he denied having any knowledge of the crimes.
“The victor will always be the judge, and the vanquished the accused.”
The ruling against him is known as the Yamashita standard, which means holding the commander responsible for the crimes done by the troops should the commander not try to discover and stop the crime from occurring.
The American troops slaughtered more than 500 people, including young girls who were raped, on March 16, 1968, in Vietnam's My Lai, which is now globally known as the My Lai massacre. But nobody was given a Yamashita standard. William Calley, who led the troops, was given three years of house arrest. The cover-up of the massacre and the failure of the military institutions to bring the culprits to justice undermined the good faith that people have in the military institutions.