After Japan bombed Pearl Harbor on December 7, 1941, it was feared the Japanese might invade and occupy the islands confiscating millions of dollars in U.S. currency. This money could be used to finance the Japanese war effort. In the summer of 1942, all normal U.S. paper money was exchanged with notes identifying specific use for the Hawaii islands. In October 1944, restrictions were lifted on these notes allowing them to be used as normal U.S. currency.
As with the Hawaii notes, there was a concern if the German military confiscated large amounts of U.S. Currency, they would use it. These notes would have been invalidated if this occurred. These were mostly used during the invasion of North Africa and Sicily.