When the war broke out with the Battles of Lexington and Concord on April 19, 1775, Knox and Lucy snuck out of Boston, and Knox joined the militia army besieging the city. His abandoned bookshop was looted and all of its stock destroyed or stolen. He served under General Artemas Ward, putting his acquired engineering skills to use developing fortifications around the city. He directed rebel cannon fire at the Battle of Bunker Hill. When General George Washington arrived in July 1775 to take command of the army, he was impressed by the work Knox had done. The two also immediately developed a liking for one another, and Knox began to interact regularly with Washington and the other generals of the developing Continental Army. Knox did not have a commission in the army, but John Adams in particular worked in the Second Continental Congress to acquire for him a commission as colonel of the army's artillery regiment. Knox bolstered his own case by writing to Adams that Richard Gridley, the older leader of the artillery under Ward, was disliked by his men and in poor health.