The Gourdou-Leseurre GL-820 HY family of four-seat single-engined floatplanes were designed and built in France during the latter half of the 1930s by Gourdou-Leseurre. The GL-820 HY and GL-821 HY 02 were shipborne reconnaissance / observation aircraft, while the sole GL-821 HY was built as a torpedo carrier.
The Gl-820 and GL-821 were low-wing monoplane floatplanes with four tandem open cockpits, (the Cockpits on the GL-821 HY 02 were enclosed). The wings, tailplanes and floats were all supported by a system of streamlined struts.