The lead ship is the first of a series or class of ships all constructed according to the same general design. Large ships are complicated internally, and may take a long time to construct, as much as five to 10 years, so it is rare to have two of them that are completely identical. The second and later ships often must be started before the first one is even launched. Nevertheless, building copies is still more efficient than building prototypes, and so the lead ship will be the one that guides the construction of the others in its class.
In the United States Navy, since the 20th century to the present, the lead ship usually lends its name to the ship class, as in Pennsylvania class battleship, whose lead ship was USS Pennsylvania (BB-38), or more recently Los Angeles class submarine named after USS Los Angeles (SSN-688). Also, hull numbers are sometimes used informally to refer to the class (such as the "688-class" in the case of the Los Angeles-class).