The O'Brien's triple-expansion steam engine — the real one, still functional, still fired up each May during the annual steaming — stood in for the doomed liner's machinery spaces in several scenes of what would become the highest-grossing film of its era. The logic wasn't hard to follow: period-correct steam machinery at that scale is not something you fabricate cheaply on a studio lot, and the O'Brien's engine room has the depth and the heat and the particular industrial weight that a set can approximate but rarely replicate. Cameron's crew dressed it, lit it, and shot it, and audiences watching in 1997 had no particular reason to think they were looking at a ship berthed a short walk from Fisherman's Wharf.

The detail circulates periodically online, the kind of local footnote that surprises people who have walked past the ship a dozen times without stopping. The O'Brien runs public tours most days, and the engine room is part of the route — the same compartment, the same gauges and valves, the same low headroom.

Anyone walking down to Pier 45 tomorrow will find the ship more or less as it always looks from the Embarcadero: dark red hull, white superstructure, the name in block letters along the bow. The engine room is one deck down, and the tour volunteers, if you ask, will tell you which part Cameron used.