1. The Battle of Marshfield took place on April 21, 1676 during King Philip's War where a small group of English colonists defended their settlement against a larger group of Native American warriors. The English emerged victorious and it marked a turning point in the war.

2. April 21, 1775 was the day after the Battles of Lexington and Concord and the Massachusetts Provincial Congress met to begin organizing the state militia for the war against Britain.

3. On April 21, 1780, the first public school in America was established in Boston, Massachusetts. Known as the Boston Latin School, it was modeled after English grammar schools and focused on classical education.

4. The Massachusetts State House was completed on April 21, 1798, marking the end of a three-year construction project. The building is still in use today as the seat of the Massachusetts state government.

5. On April 21, 1898, the U.S. Battleship Massachusetts was launched in Quincy, Massachusetts. It served in the Spanish-American War and was later decommissioned in 1921. The ship was preserved as a museum ship in 1965 and can be visited today at the Battleship Cove maritime museum in Fall River, Massachusetts.