On June 13, 1775, the leaders of the colonial forces besieging Boston learned that the British were planning to send troops out from the city to fortify the unoccupied hills surrounding the city, which would give them control of Boston Harbor. In response, 1,200 colonial troops under the command of William Prescott stealthily occupied Bunker Hill and Breed's Hill. During the night, the colonists constructed a strong fortification on Breed's Hill, as well as smaller fortified lines across the Charlestown peninsula.By daybreak of June 17, the British became aware of the presence of colonial forces on the Peninsula and mounted an attack against them that day. Two assaults on the colonial positions were repulsed with significant British casualties; the third and final attack carried the redoubt after the defenders ran out of ammunition. The colonists retreated to Cambridge over Bunker Hill, leaving the British in control of the Peninsula.The battle was a tactical victory for the British, but it proved to be a sobering experience for them, involving many more casualties than the Americans had incurred, including a large number of officers. The battle had demonstrated that inexperienced militia were able to stand up to regular army troops in battle. Subsequently, the battle discouraged the British from any further frontal attacks against well defended front lines. American casualties were comparatively much fewer, although their losses included General Joseph Warren and Major Andrew McClary, the final casualty of the battle.