Most special stamps relate to postal use and postal purposes. Stamps such as Airmails are higher denominated stamps and the extra revenue is used to defray the cost of the class of service that is being used. But War Tax stamps are a different animal entirely-they are a country using its postal service to generate revenue for another purpose, in this case war funding. The first War Tax stamps were issued by Spain in the late Nineteenth Century and War Tax stamps have been issued as late as 1974 in Bahrain. But by far the most significant use of War tax stamps was in the British Commonwealth for raising revenue for WW I. Most of the Colonial issues are overprints, but Canada produced different stamps for War Tax one of which is illustrated here. They way War Tax stamps produced revenue was that after a certain date all letters had to bear a tax stamp in addition to the postage stamp and all revenue from the sale of the tax stamps went to the war effort. The United States had a tidier solution- one that shows the close revenue relationship between the United States Post Office and the US Treasury that existed in the earlier era. The United States just raised postage rates in 1917 by 50% (from 2c for a first class letter to 3c) to help fund the war effort and this increase remained in effect for nearly two years at which time postage rates reverted to their prewar levels.