little chance of success 16C Du verloren hoop "lost troop", select soldiers to start battle
First storming party into a breach, usually volunteers under a junior officer, who drew enemy fire. Officers and sergeants who survived were usually rewarded with promotion.
a small group of soldiers that went ahead of the storming party into the breach to cover the placement of ladders etc.
A body of troops, sometimes volunteers, assigned the mission of leading an attack.
Assault or storming party with little hope of success, or if successful, little hope of survival. (Wise, Terence. Medieval Warfare, 248)
Forlorn hope is a military term that comes from the Dutch verloren hoop, which should be translated as "lost troop" although in Dutch it can also mean "lost hope". In the days of muzzle-loading muskets it was most frequently used to refer to the first wave of soldiers attacking a breach in defences during a siege. It was likely that most members of the forlorn hope would be killed or injured.