Sure, you know that the supposedly unsinkable RMS Titanic sank. In 1912, an iceberg punctured the mighty ship’s hull, and after years of speculation, the skeleton of the doomed ship was found at rest at the bottom of the North Atlantic in 1985.

The discovery was just the tip of a much more interesting iceberg, though. It turns out the deep-sea dive was a cover for a top-secret mission to find the final resting places of two Cold War submarines. That story is front and center at “Titanic: The Untold Story,” which opens Wednesday at the National Geographic Museum in Washington. The exhibition sheds new light on the groundbreaking expedition that led to the ship’s discovery.

Led by Robert Ballard, an oceanographer and underwater archaeologist, the dive took place only because of an ambitious ­barter. Ballard had developed Argo, an unmanned deep-sea camera system that gave oceanographers unprecedented access to the ocean floor. He agreed to use the technology to search for the ­remains of the USS Scorpion and the USS Thresher, two Navy ­nuclear submarines that sank during the 1960s. In exchange, the Navy financed the Titanic mission.

Ballard succeeded in all three missions, and the previously classified story anchors the exhibition. It includes artifacts such as the Alvin, the research sub that documented the wreckage of the Titanic, and memorabilia from the Scorpion’s launch.

These intriguing reminders of a once top-secret mission stand alongside artifacts from the ill-fated ocean liner, including a rare deck chair, sheet music from the band that played as the vessel sank, and the only known set of boarding tickets that survived the disaster. There’s even the Heart of the Ocean necklace, the bauble that served as a plot point in the 1997 film “Titanic.” If you want an even closer look at the exhibition, check the museum’s events page: Soon, tickets will be available for an insider tour and a chat with oceanographers, including Ballard, about how groundbreaking ocean research is changing science. The exhibition will stick around through Jan. 6.