Even after a century of constant use and the passage of more than a million ships, the great steel gates of the Miraflores locks, at the Pacific entrance of the Panama Canal, still swing open with the precision of a Swiss watch.

So exquisitely fitted and balanced are they that each of the 672-ton leaves can be moved by a pair of 25-horsepower motors. The same can be said for the massive Gatun locks on the Caribbean side. Engineered in the days of Teddy Roosevelt, their doors cast in good Pittsburgh steel, the locks—like the canal itself—were designed to handle with ease ships the size of the Titanic.

And so they can still—as long as the ships come that small.

Nowadays many