Military ones

Zippo lighters became popular in the United States Military, especially during the world wars. In World War II- when, as the Zippo Manufacturing Company's website states that, the Zippo Manufacturing Company "ceased production of lighters for the consumer markets and dedicated all the Zippo lighter production to the U.S. military". The Zippo Lighter was made of brass, but as this commodity was unobtainable due to the war effort, the Zippo Manufacturing Company turned to using steel during the war years. While the Zippo Manufacturing Company never had an official contract with the military, soldiers and armed forces personnel insisted that the PX stores carry this much sought-after lighter. Due to materials shortage during the war, Zippo Manufacturing Company had to use the more porous metal steel instead of the regular metal, brass. Since the lighter could not be finished with chrome or nickel, instead, it was covered with a special black crackle paint. A benefit of this finish is that it would not reflect the light, thereby avoiding the attention of enemy snipers. The paint, while baked on, tended to become brittle and chip off, giving the Zippo lighter a very rugged look.
The tradition from WWI of decorating lighters with coins and crude engravings, or what is referred to as "trench art" continued on with the Zippo lighter in World War II. Some of these decorated Zippo lighters were pre-war Zippos, including the 1940-41 brass Zippos with and without diagonal lines as well as earlier models. The vast majority of the lighters from 1936-1945 can be easily recognized by the rounded corners and absence of the post-1946 "canned" bottom. The bottoms are flat or protrude outwards in varying degrees even to the point that the Zippo will not stand upright on a flat surface.
During WWII the Zippo Manufacturing Company's president Mr. George G. Blaisdell shipped as many Zippo Lighters as possible to PX's and to the front line. The GI's favored the Zippo Lighters because they were inexpensive, reliable, and always worked when it was needed.
Although the Zippo Manufacturing Company have made many, many styles and finishes of the Zippo lighter since 1932, all branches of the military are recognized. Army , Navy, Air Force Marines are engraved in the different styles of the Zippo Lighter. But the recognized authentic WWII Zippo lighter is the steel cased with the black matte crackle finish.
As with all Zippo Lighters, vintage or brand new, you will always have the Zippo Lighter life-time warranty, "IT WORKS OR IT'S FIXED FREE".