Historical ISRO L37.5 liquid rocket engine identified by the GSLV-D1 mission reference as the single engine powering the GS2 second stage of the original GSLV configuration. The same official stage table records UDMH/N2O4 propellants, 720 kN maximum vacuum thrust, and a 150-second burn; no later GSLV Vikas installation is inferred here.