The cannons in the upper levels of the two blockhouses were useless. The Americans besieging Ft. Sackville at Vincennes had stationed themselves 100-150 yards out - too close for effective cannon fire and too far for the smooth-bore "Brown Bess" muskets the Redcoats and their allies used. Besides, opening the gun ports was hazardous to one's health - those frontiersmen and their rifles could easily get off a clean head shot at that range.
Unknown to the British, there were actually less Americans outside the fort than Redcoats and loyalist militia inside, but Col. George Rogers Clark, in command of the besiegers, had ordered his men to march and counter-march in and out of undulating terrain and to rotate firing positions, so as to appear more numerous. Still it had become a stalemate, and Clark knew British supply boats were on the way and could reinforce the enemy from the riverfront side. All demands for surrender of the fort at discretion were refused.
Celebratory war whoops told Clark and his men that a raiding party was coming in on the landward side, and as luck would have it, they were unaware that the town outside the fort had changed hands. A brief firefight ensued. A few were killed and a half dozen taken prisoner. Among the Ottawas, Wyandottes and Miamis taken was the famed Ottawa chief Macutte Mong.
The Indians were bound and paraded to within view of the wall along the main gate, but again beyond musket range, where they were made to kneel. Those inside the fort were invited to observe the proceedings. Either Clark or one of his officers by his order (we are still not sure today) buried a tomahawk in the back of the skull of one of the kneeling warriors. The rest began to chant their death song, as they too were similarly dispatched. Macutte Mong was last. The first strike did not kill him; it didn't even seem to disturb him. He reached up, took the tomahawk out of his own skull and handed it back to his executioner. It took two more whacks before he even keeled over. Clark put both his hands in the vast pool of blood, smeared his face with his fingers, and let out his own war whoop.
The demand for surrender was renewed and accepted.
Now before we - from the comfort of our armchairs - wag our moralistic fingers at the ghost of George Rogers Clark, let's keep a few things in mind. The commander of that fort (and the Lieutenant Governor of British Quebec) was the infamous "Hair Buyer" Hamilton. To remind him of his good fortune in being merely sent back to Virginia in irons, the scalps brought back by those warriors under his command - scalps of men, women and children on the Kentucky frontier; non-combatants all - were hung just outside where he was kept prisoner.
For a more recent perspective, talk to members of the "Greatest Generation"(as I have) who saw combat in WWII and you may find out that Waffen SS troops were often not given the same opportunities to surrender (and were treated quite differently when they did) as regular Weirmacht, though you will look in vain for paperwork confirming official sanction for such a policy. Ask Marines who island-hopped in the Pacific about "rules of engagement" (ROE) when it is quickly discovered the enemy has none.
Even today, such unlawful enemy combatants could be kept completely out of the civilian court system, placed before a military tribunal and, if found guilty, executed. (See Ex Parte Quirin, 317 U.S. 1 (1942).
In his circumstances of course, Clark had neither the time nor the inclination for such formalities.
War is messy, and often does not present itself in the clear-cut categories of a moralistic tale. To survive, you must improvise, adapt and overcome.