USS LST-821 spent the final months of World War II ferrying supplies to Western Pacific ports: Eniwetok, Okinawa, Iejima, Ulithi, Guam. She earned one battle star for her service. After Japan's surrender, she supported the occupation before sailing home and entering the reserve fleet in July 1946. Later renamed USS Harnett County after a county in North Carolina, she was recommissioned and served through the Vietnam War before being transferred to South Vietnam's Republic of Vietnam Navy as RVNS My Tho. When South Vietnam fell, the ship passed to the Philippine Navy, which gave her the name she carries to this day: BRP Sierra Madre.

In May 1999, the Philippine government ordered the Sierra Madre to be deliberately run aground on Second Thomas Shoal, known locally as Ayungin, a submerged reef 105 nautical miles west of Palawan. China had occupied nearby Mischief Reef in 1994, and Manila wanted to establish its own presence before more features were lost. Two ships were grounded that day. The BRP Lanao del Norte was later towed away at China's insistence, but the Sierra Madre stayed. President Joseph Estrada reportedly promised China the second ship would also be removed. It never was. What began as an improvised response to Chinese expansion became, by 2014, a declared "permanent installation" of the Philippine Navy. The ship that was supposed to leave became a statement that the Philippines would not.

Conditions aboard the Sierra Madre are harsh by any military standard. When BBC correspondent Rupert Wingfield-Hayes visited in September 2014, he found a garrison of eleven Filipino marines on a vessel in severe disrepair. "The ship's sides are peppered with massive holes," he reported. "Waves slosh through them right into the ship's hold." Supplies arrived by airdrop because Chinese coast guard vessels blockaded the surrounding waters. In July 2015, a Philippine Navy spokesman acknowledged the ship needed maintenance to ensure "minimum habitability." In October 2023, the government began repairs: reinforcing sleeping quarters, adding a modern kitchen, and installing internet access. Each improvement carries diplomatic weight. China has argued that the Philippines agreed not to bring construction materials to reinforce the vessel. Manila has rejected that characterization.

Resupplying the Sierra Madre has become a recurring source of confrontation. In March 2014, Chinese coast guard vessels blocked civilian supply boats for the first time, prompting Manila to airdrop provisions and later to slip a fishing boat through shallow coral where Chinese ships could not follow. The tactics escalated. In November 2021, Chinese ships blocked resupply boats again. In February 2023, the Chinese Coast Guard aimed what the Philippines called a military-grade laser at a Philippine vessel, temporarily blinding crew members. In August 2023, water cannons were fired at a Philippine Coast Guard ship. That October, Chinese vessels rammed a Philippine Coast Guard ship and a supply boat during a resupply mission. Each incident has intensified international scrutiny. President Bongbong Marcos expanded the Enhanced Defense Cooperation Agreement with the United States in February 2023, deepening the American military commitment to the Philippines.

In 2013, The New York Times visited the Sierra Madre and concluded that she would never sail again. That assessment was accurate and entirely beside the point. The ship's value is not in its seaworthiness but in its presence. Under international law, Second Thomas Shoal is a low-tide elevation within the Philippines' exclusive economic zone. The Sierra Madre provides a physical, manned platform to assert Philippine claims, a platform that cannot be dismissed as abandoned. Removing the ship would signal a retreat that no Philippine president has been willing to accept. So the vessel endures: rusting, leaking, patched just enough to remain inhabited, her hull a monument to the stubborn logic of territorial disputes where the act of staying is itself the strongest argument.