From 1931 to 1937 in the Soviet Union, extensive scientific work on rocket engine design occurred at the Gas Dynamics Laboratory in Leningrad. The well-funded and -staffed laboratory built over 100 experimental engines under the direction of Valentin Glushko. The work included regenerative cooling, hypergolic propellant ignition, and fuel injector designs that included swirling and bi-propellant mixing injectors.