From Wiki:-“The roots of the RD-180 rocket engine extend back into the Soviet Energia launch vehicle project. The RD-170, a four-chamber engine, was developed for use on the strap-on boosters for this vehicle, which ultimately was used to lift the Buran orbiter. This engine was scaled down to a two-chamber version by combining the RD-170's combustion devices with half-size turbomachinery. After successful performances in engine tests on a test stand and high-level agreements between the US government and the Russian government, the engines were imported to the US for use on the Lockheed Martin Atlas III, with first flight in 2000. The engine is also used on the United Launch Alliance Atlas V, the successor to the Atlas III.[1] The engine has similar design features to the NK-33, which was developed by a different bureau (Kuznetzov) nearly a decade earlier.” Channel 4’s Equinox did an interesting doc on engine design, how the Soviets mastered the challenges of the closed-cycle and how the NK-33 went to America.