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A forlorn hope is a band of soldiers or other combatants chosen to take the leading part in a military operation, such as an assault on a defended position, where the risk of casualties is high. The term comes from the Dutch verloren hoop, literally "lost heap", and adapted as "lost troop".^[1][2][3][4] The Dutch word hoop (in its sense of heap in English) is not cognate with English hope: this is an example of false folk etymology^[5][6][7], supported by the word in modern Dutch also bearing the meaning "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 wounded. The intention was that some would survive long enough to seize a foothold that could be reinforced, or at least that a second wave with better prospects could be sent in while the defenders were reloading or engaged in mopping up the remnants of the first wave.

A forlorn hope was typically led by a junior officer with hopes of personal advancement. If he survived, and performed courageously, he was almost guaranteed both a promotion and a long-term boost to his career prospects. As a result, despite the risks, there was often competition for the opportunity to lead the assault. The French equivalent of the forlorn hope, called Les Enfants Perdus or The Lost Children, were all guaranteed promotion to officers should they survive, so that both men and officers took up the suicidal mission as an opportunity to raise themselves in the army. By extension, the term forlorn hope became used for any body of troops placed in a hazardous position; e.g. an exposed outpost, or the defenders of an outwork in advance of the main defensive position. This usage was especially common in accounts of the English Civil War, as well as in the British Army in the Peninsular War of 1808-1814.

http://en.wikipedia.org/wiki/Forlorn_hope