I've seen the catapult on the wreck of the M2 submarine off Portland.
It seems to involve a lot of nasty pulleys & cables and a large (presumably compressed air) operated ram.
It's very easy to believe that the power of this type of catapult would be very limited.
I understand that catapult trials ("frictionless takeoff") were carried out on heavy bombers at Harwell before WWII.
Anyone know anything about those trials?