The H-I or H-1 was a Japaneseliquid-fuelledcarrier rocket, consisting of a licence-produced American first stage and set of booster rockets, and all-Japanese upper stages. It was launched nine times between 1986 and 1992. It replaced the N-II, and was subsequently replaced by the H-II, which used the same upper stages with a Japanese first stage.
The first stage of the H-I was a licence-built version of the Thor-ELT, which was originally constructed for the US Delta 1000 rocket. The stage had already been licence produced in Japan for the N-I and N-II rockets. The second stage was entirely Japanese, using an LE-5 engine. On launches to Geosynchronous transfer orbits, a Nissan-produced UM-129A solid motor was used as a third stage. Depending on the mass of the payload, either six or nine US Castor 2 SRMs would be used as booster rockets.