The Collaborative International Dictionary
Ruse \Ruse\, n. [F., fr. OF. re["u]ser, rehuser, to turn aside, to shuffle, retreat, fr. L. recusare to refuse; pref. re- again + causa cause. See Cause, and cf. Recusant.] An artifice; trick; stratagem; wile; fraud; deceit.
Ruse de guerre[F.], a stratagem of war.
Wiktionary
n. A stratagem of war.
Wikipedia
The French ruse de guerre, sometimes literally translated as ruse 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 of military 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. The term stratagem, from Ancient Greek strategema (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 the Trojan Horse in Homer's Iliad, and in well-documented events such as the flying of the American flag by the Lusitania in 1915 (while the United States was a neutral country) to deter attack by German submarines, and they also feature in fiction.
The term 'ruse de guerre' is given legal meaning within the rules of war. Good faith is required, but at least 17 different types of ruse including ambushes, false radio messages, use of spies and the use of dummy guns are considered legitimate as long as they do not involve treachery or perfidy. Landmines and similar traps are considered perfidious under the rules. Explicitly prohibited ruses under article 23 of the Hague Convention of 1907 include improper use of a flag of truce or the military insignia of the enemy.
Usage examples of "ruse de guerre".
But I am sure you know perfectly well that it is a legitimate ruse de guerre to fly another flag as long as it is lowered and one's own flag hoisted before opening fire.
By way of a ruse de guerre he had somehow acquired a clergyman's hat, and this, combined with his earrings, his yard of pigtail, his watchet-blue jacket with brass buttons, his white trousers and low silver-buckled shoes, succeeded so well that several customers followed him from the tap-room to gaze while he leaned in and said to Jack, 'It's no go, sir.
By way of a ruse de guerre he had somehow acquired a clergyman’.
And there are all those Italians, and the poor dear Pope: and only the very day before he left, Jack mentioned Pappenburg -he had hoisted the flag of Pappenburg, by way of a ruse de guerre.
That had been a legitimate ruse de guerre for which historical precedents without number could be quoted, but the French government had apparently deemed it a violation of the laws of war.
Our captain, who was a man of the most consummate ruse de guerre I ever saw or heard of, had two reasons for sending his prizes to Gibraltar.
He felt for him now: but, he reflected, Stephen's was at least an honourable secrecy, a long-drawn-out permissible ruse de guerre that could not damage him in his own opinion.