The Army of Oz is the military force of the Fairyland known as the Land of Oz.
During the reign of the Wizard of Oz the army consisted of one man, the Soldier with the Green Whiskers. Although he carried a gun, he never kept it loaded for fear of it going off. (The Wonderful Wizard of Oz)
When Ozma ascended to the throne, she expanded the army. On her mission to free the Royal Family of Ev from the Nome King, she brought an army consisting of twenty-seven soldiers: eight generals, six colonels, seven majors, five captains, and one private. Some were lean and some fat, some were tall and some short. But all wore handsome uniforms of various designs and colors, no two being alike. The mission ended successfully, and Omby Amby the private was promoted to Captain General of all the Armies of Oz, leaving only two other privates in the royal armies. (Ozma of Oz)
By the time of Ozma's birthday, the army was composed of twenty seven men without a single private. (The Road to Oz)