This is 100% about continuing the vassal relationship, the more strategic ties between US-Japan the harder it will be to even begin to suggest Japanese independence.
The technology in question here is most likely irrelevant, but as we know its not about real world impact but the perception of it, you convince the entire capitalist-political class these shit weapons actually work and they'll act accordingly. You convince Japan that they've contributed and now share extremely critical strategic/military/technological ties with the US MIC and they'll believe it, even though it could literally be about making a van to sell ice cream, convince those idiots its actualy a super tank and away they go.
List of Brazilian inventions