On February 26, 1775 men under Pickering's command were involved in one of the earliest military engagements in the American Revolution, a confrontation locally referred to as "Leslie's Retreat." A detachment of British regulars under British Army Lt. Colonel Alexander Leslie was dispatched from Boston to search North Salem for contraband artillery. Leslie's men were thwarted from crossing the North River bridge and searching the outlying farms by Pickering's militia and citizens of Salem. Many of these "citizens" were members of Salem's North Church, which was just a short distance from the North Bridge. Col. Leslie chose a Sunday morning to raid Salem knowing that her citizens would be attending church. They were, of course, but the Rev. Thomas Barnard Jr. of the North Church famously left his pulpit that morning to meet the British troops at the bridge. A fast rider from Marblehead had ridden ahead of the British to warn Mr. Barnard. Barnard is credited with convincing Col. Leslie to retreat in peace. If he had not, Pickering's troops would have fired the "shot heard 'round the world" and started the war. Two months later, Pickering's troops marched to take part in the Battles of Lexington and Concord but arrived too late to play a major role. They then became part of the New England army assembling outside Boston to lay siege to the city.