The U.S. believes North Korea's short range missile launches last month were to advance its missile technology.
In its recent report on the North's nuclear and missile program,... the U.S. Congressional Research Service defined last month's missiles as short range (quote)"ballistic missiles" and said,... the regime launched them to advance its solid-fuel engine and guidance system technology.
It analyzed that the North is slowly moving from liquid fuel to solid fuel missiles... adding that the regime is focusing on neutralizing missile defense systems like Patriot, Aegis, and THAAD.