American forces built extensive military fortifications across Bora Bora during World War II, when the island served as a major supply and refuelling base in the Pacific. The most dramatic remains are the large naval gun emplacements at several points around the island's perimeter — the guns themselves are still in place, rusted but intact, pointing out toward a war that never reached them.
The guns at Fitiiu Point on the north coast and at Matira Point at the southern tip are the most accessible. A jeep tour (available from several operators in Vaitape) is the best way to see them all, as the emplacements are scattered around the island and not easily walked between. The jeep tour typically takes three to four hours and includes historical commentary — a surprisingly compelling half-day for what is marketed primarily as a resort destination.