Up until the early 1960s, catapult launches were accomplished by connecting the aircraft to the catapult shuttle with a heavy cable, called a pendant or a bridle depending on the hookup configuration. A separate hookup held the aircraft from moving even under full power until the catapult fired and a weak link in the holdback failed with the increase in pull.
This was hard, dangerous work. The cables were heavy and the hookup point on the aircraft generally uncomfortably close to the jet engine inlets or the propellers. The holdback connection was under the aft fuselage, just forward of the jet engine exhaust, a dark, dirty, noisy place, usually requiring a very low squat to access the fuselage hookup point.
The replacement was the addition of both the catapult and holdback hookups onto the nose landing gear. Grumman developed the concept and introduced it with A-6 Intruder and the E-2 Hawkeye. The launch bar was located on the front of the nose gear strut and could be raised and lowered by the pilot; the holdback connection was on the aft side of the nose gear strut.
The pilot simply taxied forward onto the catapult hook up point and lowered the launch bar. The green shirts then attached the holdback bar (color coded for each aircraft type) to the aircraft and the deck and signaled for the shuttle to be moved aft until the front end of the launch bar was positioned in the cavity at the front of the shuttle. The shuttle was then moved forward to fully engage the launch bar and establish tension. Once the pilot was ready; full takeoff thrust applied; and final checking accomplished, the catapult was fired; the holdback connection released (leaving the holdback bar on the deck); and the aircraft was on its way.
The two different launch hookups coexisted for a time, since retrofit of the concept would have required extensive structural modification to the aircraft. Eventually, however, the last of the pendant/bridle-launched aircraft was retired.