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When the Revolution's stirrings began, the Provincial Congress required the militia to have chaplains. Spring took up his colony's call. He served in both the Siege of Boston and in the invasion of Canada. He initially served in the regiment commanded by Colonel John Fellows of Sheffield. Burr also served at the Siege of Boston. When Colonel Benedict Arnold convinced General George Washington to open a second front against the British in Canada, Spring and Burr both joined this force under Colonel Benedict Arnold. Ships sailed from Newburyport, Massachusetts to Maine. At Fort Western, near what is now Augusta, Maine, Spring counseled Private James McCormick, who was sentenced to death, only to be reprieved.