Overview
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 identical. Constructing one ship is also likely to reveal better ways of doing things and even errors.
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.
Read more about this topic: Lead Ship