ThesiegeofBoston,whichstartedinApril1775,wastheopeningphaseoftheAmericanRevolution.TheAmericans,ledbyGeneralWashington,surroundedthecity,butforalongtimenoseriousoperationswereundertaken.Then,onemorninginJanuary1776,whentheBritishawoke,theywereshockedtofindthatthehillsoverlookingBostonwerebristlingwithcannons,readytoblowthemtokingdomcome.
TheBritishdecidednottofight,andsentamessagetoWashingtonsayingthatiftheywereallowedtoleaveunmolested,theywouldnotburnthetown.Washingtonagreed.
WhattheBritishdidnotrealisewasthatWashingtonsimplydidnothavethegunpowderrequiredtofirethecannons.TheAmericansweresoshortongunpowderthatsoldiersweregivenaspeartofightwithintheeventofaBritishattack!
一七七五年四月展開的波士頓圍城戰，是美國獨立戰爭的序幕。美軍由華盛頓將軍率領，包圍了波士頓，但雙方長時期沒有嚴重衝突。到了一七七六年一月，英軍一天早上醒來，看見俯臨波士頓的群山滿是大炮，隨時可以把他們轟到西天，不禁大驚。
英軍決定不接戰，遣使告訴華盛頓說，只要美軍不阻礙他們撤走，就不放火燒城。華盛頓答應了。
英國人不知道的是，華盛頓根本沒有火藥發炮。美軍當時非常缺乏火藥，士兵都獲發長矛，準備英軍進擊就用來對敵。