They may look like Christmas tree ornaments—but their origin is a bit deadlier. While they now sport beautiful decorative paintings depicting Mount Fuji through the four seasons, these colorful orbs actually began their existence as World War II hand grenades.
Type 4s, or ceramic grenades, were produced by the Imperial Japanese Navy in the waning days of the war as the raw materials of conflict, such as metals, were in ever-rarer supply. As the noose tightened and Japan prepared to defend the Home Islands to the last man, these crude, porcelain-encased fragmentation explosives were cranked out and distributed en masse to home-front reservists, volunteer defense groups, and the like. They also made their way to the beleaguered front lines, adding to the din at Iwo Jima and Okinawa. Revered pottery kilns famous for their exquisite Japanese export pottery were mustered into the war effort to mass-produce the cheap boomers. Measuring approximately 4 inches in height and 3 inches in diameter, they employed a simplistic firecracker-like fuse, a rubber cap, and a glorified blasting cap as a detonator.