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.