Although the H-I did have some domestically produced components, such as LE-5 engine on the second stage and inertial guidance system, the most crucial part, the first stage engine, was a licence-built version of the Thor-ELT of the US.
The H-I launch vehicle had some domestically produced parts, including the LE-5 engine for its second stage and an inertial guidance system. However, the key component, the first stage engine, was a copy of the US-made Thor-ELT.