大尉 is mostly used in translations of foreign (especially Russian/Soviet and old Japanese imperial) ranks. The PRC's PLA replaced
大尉 with
上尉 (shàngwèi, "senior captain") in the 1965 rank reform, so in modern Chinese army contexts you'll see
上尉. In subtitle data
大尉 typically tags a Russian Капитан or Japanese
大尉 (taii).