During the First World War (1914-1918) the machines of the Swiss Mint were working at full speed night and day. Paper money was increasingly issued as well; the Swiss Federal Council declared banknotes as legal tender and lifted the obligation of the National Bank to exchange bills against precious metals. In this way, paper money gained effective significance during the War for the first time. Toward the end of the War, Switzerland decided the issue of coins from brass. Nickel, which had hitherto been used for minor coins, had become scarce, as it was needed for armament. In 1923, however, the brass coins were withdrawn from circulation and replaced by nickel coins once again.