The most direct way to describe Flamenco Beach is that it is the best beach in the Caribbean that the United States once used for target practice. Both halves of that sentence are literally true, and the second one is the reason the first one is worth a page.

The beach. Flamenco is a horseshoe bay about a mile long on the northwest coast of Culebra, a small island 27 kilometers off mainland Puerto Rico. The sand is bright and fine, the reef shelters the bay so the water stays shallow and calm, and the color is the postcard turquoise. In 2014 TripAdvisor's Travelers' Choice awards ranked it the third-best beach in the world, and it has stayed in the global top fifteen in most years since. There are no hotels on it. The development is a campground and a row of food kiosks. By the standard checklist of a great Caribbean beach, the only thing Flamenco is missing is a flaw.

The range. From 1939 until 1975 the US Navy used the Culebra archipelago as a gunnery and bombing range, and Flamenco Beach sat inside the impact area. The lineage goes back further: Theodore Roosevelt established the Culebra Naval Reservation in 1903, putting the island under Navy control at the start of the century. Through the Second World War and the Cold War the range grew, and US naval exercises here peaked in 1969, with ships and air units of the Atlantic Fleet attached. For more than three decades, the beach that now tops best-of lists was a place the Marines fired live rounds at parked armor.

The tanks. That armor is still here. Two M4 Sherman tanks used as stationary live-fire targets sit at the western end of the sand, where the Marines left them in 1975. The salt air has been working on them for half a century; they are half-collapsed, deeply corroded, and held together visually by layers of graffiti that locals and visitors repaint continually. They are the single strangest thing on any world-class beach, war machines a few hundred meters from the swimming families, and Culebra has chosen to keep them. They were not missed by a cleanup. They are a monument the island decided not to remove.

How the Navy left. It did not leave voluntarily. In 1971 the people of Culebra, joined by the Puerto Rican Independence Party under Rubén Berríos and by Catholic and Protestant clergy committees, began a campaign of civil disobedience against the bombing. Their sharpest act was to build a small ecumenical chapel on Flamenco Beach, inside the live range, after the military had demolished an earlier structure. Berríos and thirteen others were arrested for trespassing on US military property and sentenced to three months in prison; Berríos was expelled from his professorship at the University of Puerto Rico law school as a consequence. The protests ran four years. In 1975 the Navy ceased operations on Culebra and shifted its bombing to the neighboring island of Vieques, where the fight would resume and continue until 2003. Culebra was the first round of a longer war, and the island won it.

Roosevelt's double legacy. The same president who made Culebra a naval reservation in 1903 also made part of it a federal bird refuge in 1909, one of the oldest in the United States. That refuge survived the bombing years and still borders Flamenco. Each summer it protects roughly fifty thousand seabirds, sooty terns among them, nesting on the Flamenco Peninsula, and the leatherback, green, and hawksbill turtles that come ashore on the refuge beaches. The contradiction is total and it is on one island: the same archipelago, ordered by the same man, was made into both a place to drop bombs and a place to protect nesting birds.

What is unresolved. The reclaiming is not finished. Large parts of Culebra remain a Formerly Used Defense Site, and the US Army Corps of Engineers has spent decades clearing unexploded ordnance left from the range. The main beach is safe; the backcountry and the old impact zones are posted, and live shells still surface. And the victory has a modern cost: the rankings that made Flamenco famous now send day-trippers to an island of 1,792 people running on one ferry and a thin water supply. Culebra fought the most powerful navy on earth to keep this beach undeveloped, and the prize for winning is a crowd the island was never built to hold.

What it is. Flamenco is not a paradise with a dark footnote. It is a place whose beauty and its history cannot be separated, because the reason it stayed undeveloped is that it was a weapons range and then a refuge instead of a resort strip. The tanks at the tree line are not an eyesore on a perfect beach. They are the point. They are how the island tells you, in rusted steel and spray paint, exactly what this water used to be and exactly who took it back.