Nothing new. This has been common in the US for decades. I'm actually rather surprised that this is new for Japan, which has a mature defense industry. They even produce their own air-to-air missiles, tech right at the heart of the matter.
"In 2017, the United States Patent and Trademark Office (USPTO) reported statistics that there were over 5,700 classified patents held by the United States government. These inventions are highly guarded under sensitive secrecy orders. The public may never know more about these classified inventions, but some once-secret patents included a laser-tracking system, a stronger net, and a warhead-production method.
Invention secrecy dates back to the 1930s, but exploded in the 1940s when nuclear weapon development became a highly classified topic. Under the Invention Secrecy Act of 1951, federal law prevented the disclosure of new technologies and inventions that may present a national security threat to the United States."
https://www.upcounsel.com/classified-patents
"In 2017, the United States Patent and Trademark Office (USPTO) reported statistics that there were over 5,700 classified patents held by the United States government. These inventions are highly guarded under sensitive secrecy orders. The public may never know more about these classified inventions, but some once-secret patents included a laser-tracking system, a stronger net, and a warhead-production method.
Invention secrecy dates back to the 1930s, but exploded in the 1940s when nuclear weapon development became a highly classified topic. Under the Invention Secrecy Act of 1951, federal law prevented the disclosure of new technologies and inventions that may present a national security threat to the United States."