As the American force continued to gather around Boston during the siege, they realized that they did not have the munitions or cannon to carry out successful siege or military operations. Fort Ticonderoga, which is located on Lake Champlain, became an objective for its stores of munitions and the strategic position of control that it held over the waterways to Canada.
As a result, expeditions began to be planned to capture the fort. Col. Benedict Arnold proposed the capture of Ticonderoga and Crown Point, and the plan was approved by Dr. Joseph Warren, chairman of the Committee of Safety. Arnold was commissioned as colonel by the Provincial Congress of Massachusetts. He was directed to raise 400 troops in the western counties and surprise the forts. The same scheme had been entertained in Connecticut, and troops from that colony and from Berkshire, with a number of "Green Mountain Boys," had already started for the lakes under command of Col. Ethan Allen. Allen was made colonel of an armed force known as the "Green Mountain Boys," raised in order to protect holders of land granted by New Hampshire. He was declared an outlaw, and £150 was offered for his capture by New York's Gov. ?? Tryon.
Upon meeting them, Arnold claimed the command, but when it was refused he joined the expedition as a volunteer and entered Fort Ticonderoga side by side with Allen. A few days later, Arnold captured St. John's. Massachusetts asked Connecticut to put him in command of these posts, but Connecticut preferred Allen.
When Arnold learned of Allen's expedition, he left his men behind and hurried to catch up with Allen. Arnold caught up with Allen and tried to take command of the expedition on the authority of the Massachusetts Committee of Safety, but since he had none of his own men and the Green Mountain Boys would not follow him, it was agreed that the 2 men would share command.
On May 9, Benedict Arnold arrived in Castleton and insisted that he was taking command of the operation, based on his orders and commission from the Massachusetts Committee of Safety. Many of the Green Mountain Boys objected, insisting that they would go home rather than serve under anyone but Ethan Allen. Arnold and Allen worked out an agreement, but no documented evidence exists about what the terms of the agreement were. According to Arnold, he was given joint command of the operation. Some historians have supported Arnold's contention, while others suggest he was merely given the right to march next to Allen.
On May 10, at dawn, the Patriots slipped into the fort. Most of the dozen British soldiers garrisoned there were still asleep. As dawn approached, fearful of losing the element of surprise, they attacked. Surprising the only sentry on duty at the south gate, they rushed into the fort. Allen and Arnold charged up the stairs into the officer's quarters and demanded surrender, which they got. As they entered the officers' quarters, Allen is said to have yelled, "Come out of there, you damned old rat!" Although in his memoirs, Allen later wrote that he had said, "in the name of the Great Jehovah and the Continental Congress." The commander of the fort appeared and quickly surrendered the fort.
Fort Ticonderoga was not the fortress it had been in 1758. It had largely fallen into disrepair and the garrison consisted of only 2 officers and 50 men. But, it still had a large stock of artillery. Only one shot was fired, and there were no serious injuries on either side. Both American leaders were ordered to take the approximately 100 cannon stored in the fort. They did not arrive in Boston until January 1776.