Eagle Crest United States Navy Shellback Challenge Coin 3097 Magnificently detailed, 2 sided bronze challenge coin. This is the new, updated version of a classic challenge coin. Officially licensed United States Navy logo on one side. "Shellback...Crosing The Line" with King Neptune and ocean scene on the other side 1.7 inch diameter, 0.125 inches thick A "Shellback" is a person who crosses the Equator for the first time. It's a really big deal!