Fort Serapong, one of four key fortifications on Sentosa Island, played a vital role in Singapore's southern coastal defense. Built between the 1870s and 1890s atop Mount Serapong, the island's highest point, it offered a strategic vantage for monitoring threats. Originally a swamp, the area was transformed into a military site, becoming crucial after the demolition of Fort Fullerton, Fort Palmer, and Fort Tanjong Katong. From the early 1900s to the 1930s, it saw heavy gun practices, with large red flags signaling exercises. Upgraded in the 1930s, Fort Serapong gained advanced weaponry and improved observation and coordination facilities. Today, it stands as a testament to Singapore's military history and Sentosa's strategic significance.