Off the north coast of Ireland, the Queen Mary had about ten thousand American troops aboard and orders not to stop for anything, submarines being the whole reason Curacoa was there at all. The two ships were zigzagging to different patterns, and the liner's bow came through the cruiser abreast of her after funnel and cut her in two. That was 1942, and 337 of Curacoa's crew were lost; the destroyers picked up a little over a hundred, her captain among them. The Queen Mary went on, as she had been told to.
She had four sets of Parsons geared turbines, somewhere around 160,000 shaft horsepower, and could hold close to 28 knots — faster than a surfaced U-boat, which is why the standing order was to keep running whatever happened astern. Curacoa, built in 1917, had no way to match that over any distance.
The two zigzags were the heart of it — each ship was keeping a legitimate pattern, but they were different patterns, so the legs could swing them onto converging courses with neither bridge seeing it as closing. A sound precaution against submarines that left very little room between the two hulls.