Neutral military observers closely studied landing tactics and operations during the War of the Pacific: two Royal Navy ships monitored the Battle of Pisagua; United States Navy observer Lt. Theodorus B. M. Mason included an account in his report "The War on the Pacific Coast of South America". The with Alfred Thayer Mahan in command, was stationed at Callao, Peru, protecting American interests during the final stages of the War of the Pacific. He formulated his concept of sea power while reading a history book in an English gentleman's club in Lima, Peru. This concept became the foundation for his celebrated "The Influence of Sea Power upon History" (1890).