GCA

Abbreviation for Ground Controlled Approach. A controller, traditionally on the ground (but clearly, aboard ship also meets the definition), provides radar guidance to the pilot to enable him to fly the aircraft on the correct track and glidepath of without the use of onboard navigational aids.

GCAs were the first precision approach procedure in instrument flying, and were most famously used during the Berlin Airlift in 1948. Not until the Instrument Landing System (ILS) became common were precision approaches widely available where GCA facilities didn't exist.