The Joong Ang Ilbo has an article that takes an indepth look at the UNC’s rear bases in Japan and what their functions are:
The recent visit to the United Nations Command (UNC) rear base in Japan represents a continuation of the Korea Peace Foundation’s ongoing quest for peace in Northeast Asia since its establishment in 2015.
Joong Ang Ilbo
Established in 1950 in the aftermath of the 1950-1953 Korean War, the UNC has been instrumental in preventing further conflict and upholding peace on the peninsula by maintaining the armistice and deterring North Korean aggression.
The UNC extended its presence to Japan to uphold these objectives.
The Peace Odyssey’s trip marked the first time the UNC granted foreign civilians access to its rear bases in Japan since the Covid-19 pandemic.
There are seven UNC rear bases in Japan. The Peace Odyssey visited two — the Yokosuka Naval Base and the Yokota Air Base.
While the UNC has made most base facilities accessible, a few remain off-limits. Amid the rapidly evolving international landscape characterized by increased cooperation between North Korea, China, and Russia, the UNC sought to provide accurate information about its role.
You can read the rest at the link, but as the article mentions the UNC rear bases in Japan serves a lot like what Kuwait has served for operations in the Middle East. Japan’s bases would be a critical logistics hub for bringing in material and troops to support any contingency on the Korean peninsula.