Titanic's ocean scenes were shot in a tank built just for the film.

For James Cameron’s 1997 film Titanic, no existing studio in the world had a tank large enough to hold a near-full-scale replica of the ship. Production company Fox built an entirely new studio on the Pacific coast near Rosarito, Mexico, centered on a purpose-built water tank holding around 17 million gallons.

The facility, later known as Baja Studios, was constructed specifically for the production and has since been used for other large-scale water filming, including sequels in the Fast & Furious franchise.