During the Buran programme initial development of the 11D77 —the launch vehicle later known as Zenit—, KBKhA had been assigned the development of the second stage engine, as they had done for the Proton and Soyuz vehicles. But given the difficulties for NPO Energomash in developing the RD-123 (which would later be known as the RD-170), they ceded the hydrogen / oxygen sustainer engine development to KBKhA. This project, the analog of the SSME, was project RD-130 within NPO Energomash. But when KBKhA tackled the development, named it RD-"0"120, a name that is always a source of confusion with the engine of the current article. In exchange for them tackling the difficult development of the cryogenic propellant engine, Energomash assumed the responsibility of developing the second stage engine of the 11D77, which would eventually be known as the RD-120. The fact that the RD-120 and the RD-0120 had this intertwined conception, within the same program, and with a swap of designer bureaus, does not help to avoid the confusion.