In 1899 the regiment deployed to the Philippine Islands to help suppress a guerrilla movement in the Philippine-American War. The regiment returned to the Islands in 1905 and 1911. Though the 24th fought a number of battles in the Philippines, one of the most notable occurred on 7 December 1899, when nine soldiers from the regiment routed 100 guerrillas from their trenches.
Question: How many years passed between the regiment's first and second return?
Answer: 6