What’s a catapult ship?
Before navies started using helicopters, some ships would carry one or two small airplanes on board. These ships wouldn’t be actual aircraft carriers, though, and would lack the big flat decks for landing and take-offs. So they would have a rail across the deck that they would mount the airplane on, and by means of hydraulics or pneumatics or rockets or whatever they would launch the airplane along the rail and off the side of the ship. If all went well, the airplane would then be airborne.
This would then let the people on the ship know what was going on over the horizon, as the airplane would have a radio and could go scouting around. It could also spot submarines and things like that.
Of course, the airplane couldn’t land on the ship afterward. Either the airplane would have floats on it so that it could land in the water near the ship and be hauled on board with cranes, or it would fly off and land on a proper aircraft carrier or airfield on land, or else it would be a really cheap disposable airplane that the pilot would jump out of in mid-air and he’d hope to parachute down to the ship while the airplane crashed into the water.
If you look at pictures of the WWII German navy’s ship Bismarck, you can see the catapult track near the middle of the ship stretching from one side to the other. You can also often see the airplane mounted on it.
Of course, the USS Pine Island mentioned in the above article wasn’t actually a catapult ship, but that’s only a minor little detail. . .