Ever since the 2nd century B.C. -- not long after Romans began minting coins -- shipbuilders have been slipping a coin into the structure of their ships. It’s a tradition that continues today. In fact, the USS New York - made partially from steel recovered from the World Trade Center towers - did it as well (Stepping the Mast is an ancient tradition where coins are placed under or near the mast when the mast is installed. The coins are intended to bring the ship good luck. The Navy and shipyard continue this tradition today and usually use coins, which add up to the ship's hull number, e.g. 17 cents for LPD 17).You can read more about the coin (a George II half-penny) at Discovery.com.