The Oerlikon GDF or Oerlikon 35 mm twin cannon is a towed anti-aircraft gun made by Oerlikon Contraves. The system was originally designated 2 ZLA/353 ML but this was later changed to GDF-001. It was developed in the late 1950s and is used by around 30 countries.

Rheinmetall Air Defence AG is a division of German armament manufacturer Rheinmetall, created when the company's Oerlikon Contraves unit was renamed on 1 January 2009 and integrated with Rheinmetall's other air-defence products. Oerlikon Contraves was a Swiss anti-aircraft artillery manufacturer famous for its adaptation of the 1916 20 mm Becker as the Oerlikon 20 mm autocannon design, which was used in the Second World War and still in use today. Copies and derivatives of these designs were made by German, French, British, and Japanese weapon manufacturers. Oerlikon Contraves was purchased by Rheinmetall in 1999.