1. In 1980, the eruption of Mount St. Helens in Washington had a significant impact on Montana. The ash cloud from the eruption reached as far east as Billings and caused disruptions in air traffic and agriculture.

2. On May 18, 1896, mining magnate Augustus Heinze organized the Montana Ore Purchasing Company in Butte. The company's initial success would eventually lead to a bitter legal battle between Heinze and copper king William A. Clark.

3. In 1904, Montana Governor Joseph K. Toole signed a bill establishing the Montana State Normal School (now known as Montana State University-Billings) in Billings. The school was intended to train teachers for the state's growing population.

4. May 18, 1887, saw the birth of author Olaf Baker in Beaverhead County. Baker is known for his historical fiction set in the American West, including the book "Blood on the Moon," which was adapted into a film starring Robert Mitchum.

5. On May 18, 1943, the submarine USS Puffer sank off the coast of Alaska with all hands, including Montana-born Lieutenant Commander Donald McGregor. The cause of the sinking remains a mystery.