1. On May 12, 1780, the Battle of Fort Royal took place during the American Revolutionary War. British forces, led by Sir Henry Clinton, attacked Fort Royal (located in what is now Castine, Maine) which was defended by Massachusetts troops with the assistance of the Penobscot tribe. The British were successful in capturing the fort, which remained under British control for the rest of the war.

2. On May 12, 1871, the Great Fire of Portland destroyed much of the city's downtown area. The fire began in a bakery and quickly spread due to high winds and dry conditions. Over 1,500 buildings were destroyed and 10,000 people were left homeless. Despite the devastation, the city was rebuilt in brick and stone, which helped prevent similar fires from occurring in the future.

3. May 12, 1921 marked the opening of the Maine State Pier in Portland. The pier was designed to accommodate larger ships and to handle the increasing amount of freight traffic in the area. The pier played an important role in Maine's economy for many years, but by the 1970s it had fallen into disrepair. In the early 2000s, the pier was renovated and is now a popular destination for tourists and locals alike.

4. On May 12, 1958, the USS Nautilus became the first submarine to navigate under the Arctic ice pack. The Nautilus was designed and built at the Portsmouth Naval Shipyard in Kittery, Maine, and was named after the fictional submarine in Jules Verne's novel "Twenty Thousand Leagues Under the Sea." The submarine's historic voyage helped pave the way for future exploration and research in the Arctic region.

5. May 12, 2015 saw the opening of the new Veterans Memorial Bridge in Portland, replacing the old Veteran's Memorial Bridge which had been in use since 1954. The new bridge features wider lanes, bike lanes, and a pedestrian walkway, and was built to accommodate increasing traffic in the area. The bridge also honors Maine's veterans with a large stone monument at the eastern end.