I am just wondering out loud here, so please take no offense anyone.
But after WW II when Japan disarmed and became effectually pacifist, the Japanese Army and Navy, from my point of ignorance, are awfully small and would possibly be little more than a speed bump if China became hostile.
Is the above announcement perhaps Japan coming to the realization that they are vulnerable to the Chinese and couldn't defend "disputed" waters/islands that China now covets to their own ends?
It seems to me what China has been doing in the South China Sea (and really, elsewhere in the world-Africa for instance) is not a whole lot different than what Japan, Germany attempted in the 30's.
Anyway, Japan could certainly do with an upgrade.