When my wife and I visited Japan in 2007 we stayed with our in-laws that were housed in Sagamihara, a US military installation. My SIL worked for Department of Defense and had a 5 year contract to work in Japan. She got to bring her useless out-of work husband with her.
They get to stay rent free and had COLA. All on the dime of me and you and countless Americans.....
Anyway I digress. I was going to say the Security for the "Base" is under the control of the Japanese government. So even though it's a US Installation the Japanese get to do the security.
So anyway entering into the base they will stop your vehicle and check your credentials (passports for me and wife) before you can enter. If there is a public bus that needs to enter the base they will stop the bus and 2 or 3 of these security "commandos"
will enter to check ID's and passports.
The security guards carried shotguns. It is slung over their shoulders but they are menacing looking things. The guards are very polite, smiling even as they go through what is an everyday normal procedure.
One day my SIL who can talk a little Japanese struck up a conversation with one of them. He smiled and shook his head and waved his hand.
She later told us that she asked him if the weapon is loaded. He smiled and said no.
I wouldn't be surprised because the base is basically a residential facility but again, maybe he just said that to put her at ease.