Japan does have an army. Its just called a (Japanese) Self Defense Force................but its an army leashed by the US for their actions in WWII.
As an army, they can only be effective if we help them. But they are definately packing some significant firepower.
They are green as green can be though, and lack battle tested officers. They would be inefficient without our support and elements from our airforce, navy, artillery, and officer corps. Luckily, with all the crazies in the error shooting rockets over their country, they are quickly becoming pretty solid with us. Their WWII generation and their kids hated us for nuking their country.