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The lead ship or class leader is the first of a series or class of ships all constructed according to the same general design. Almost always, this is only applicable for military ships and larger civilian craft.

Large ships are complicated internally and may take as much as five to ten years to construct. Any changes or advances that are available when building a ship are likely to be included, so it is rare to have two that are completely identical. Constructing one ship is also likely to reveal better ways of doing things, and even errors. For example, when the United States built the USS Ohio as the lead ship of her class of submarines, they found that the access hatches were not large enough to load some internal components only after construction was nearly complete.^{[citation needed]}

The second and later ships are often started before the first one is completed, launched and tested. Nevertheless, building copies is still more efficient and cost-effective than building prototypes, and the lead ship will usually be followed by copies with some improvements rather than radically different versions. The improvements will sometimes be retrofitted to the lead ship. Occasionally, the lead ship will be launched and commissioned for shakedown testing before following ships are completed, making the lead ship a combination of template and prototype, rather than expending resources on a prototype that will never see actual use.

Ship classes are typically named in one of two ways; echoing the name of the lead ship, such as the Pennsylvania-class battleships, whose lead ship was USS Pennsylvania, or defining a theme by which vessels in the class are named, as in the Royal Navy's Tribal-class frigates, named after tribes of the world, such as HMS Mohawk. If a ship class is produced for another fleet, the first active unit will become the lead ship for that fleet; for example, the Oliver Hazard Perry-class frigates are known as the Adelaide-class in the Royal Australian Navy. Larger civilian craft, such as the Pacific Sun, the lead ship of the Sun-class cruise ships sometimes follow this convention as well.

The same custom is often followed in fiction: the Constitution-class cruiser is the basis for the Enterprise of Star Trek, and the Eclipse-class Star Destroyer appears in Star Wars.

1. Example of a lead ship announcement from US Navy
2. The USS Pennsylvania BB-38