The Country Needed Copper
When Japan attacked Pearl Harbor, the United States was not willing to take chances. The country wanted to make war supplies right away. However, this meant that it needed a lot of copper. After all, this material was very important when it comes to the production of bullets, weapons, and the like.
No Copper For Civilian Use
It did not help that copper was growing scarce at the time. This was the reason the United States government decided to ban the use of it for civilian use. Aside from that, it also began to produce coins using other materials. As you can see, the government went to great lengths to manufacture more arms.