Sub-hydrant?

Walking towards Machida train station one morning I noticed what I at first thought were man-hole covers but then realized that they are too small for anybody to fit into. They have what is obviously a "key" hole along the bottom edge and, since they are adorned with images of fire apparatus (that's "trucks" for all you pedestrians), I've come to believe that they must be covering access to a below-ground water pipe. If so, it's quite clever; easy identification for the firefighting crews and instead of a hydrant sticking up out of the ground where it is exposed to vandalism and/or accidents, the hose-coupling lies flush with the street.

But what the heck do I know? I'm just hazarding a guess.