Dawes was assigned by Doctor Joseph Warren to ride from Boston, Massachusetts, to Lexington on the night of April 18, 1775, when it became clear that a British column was going to march into the countryside. Dawes's mission was to warn John Hancock and Samuel Adams that they were in danger of arrest. Dawes took the land route out of Boston through the Boston Neck, leaving just before the military sealed off the town.
Also acting under Dr. Warren, Paul Revere arranged for another rider waiting across the Charles River in Charlestown to be told of the army's route with lanterns hung in Old North Church. To be certain the message would get through, Revere rowed across the river and started riding westwards himself.
Dawes and Revere arrived at the Hancock-Clarke House in Lexington about the same time, shortly after midnight. In fact, Revere arrived slightly earlier, despite having stopped to speak to militia officers in towns along the way, because his ride was shorter and his horse faster. After warning Adams and Hancock to leave, Revere and Dawes chose to proceed to Concord in case that was the British column's goal. Revere no doubt knew that the Provincial Congress had stored munitions there, including the cannon Dawes had helped to secure. Along the way, the two men met Samuel Prescott, a local young physician, who joined them.
A squad of mounted British officers awaited on the road between Lexington and Concord. They had already arrested some riders heading west with news of the troops, and they called for Dawes, Revere, and Prescott to halt. The three men rode in different directions, hoping one would escape. Dawes, according to the story he told his children, rode into the yard of a house shouting that he had lured two officers there. Fearing an ambush, the officers stopped chasing him. Dawes's horse bucked him off, however, and he had to walk back to Lexington. He later said that in the morning he returned to the same yard and found the watch that had fallen from his pocket. Otherwise, Dawes's activity during the Battle of Lexington and Concord remains unknown.
Dawes and his companions' warning allowed the town militias to muster a sufficient force for the first open battle of the Revolutionary War and the first colonial victory. The British troops did not find most of the weapons they had marched to destroy and sustained serious losses during their retreat to Boston under guerrilla fire.
However, as I mentioned in the lead, Paul Revere had a better marketing firm (H. Longfellow, inc.) than Dawes (Helen F. Moore, Inc. 30 years late and a dollar short). As Malcolm Gladwell said in The Tipping Point, Revere was a "connector" while Dawes was just an "ordinary man."