Sister ship

Such vessels share a nearly identical hull and superstructure layout, similar size, and roughly comparable features and equipment.

Often, sisters become more differentiated during their service as their equipment (in the case of naval vessels, their armament) are separately altered.

All three were converted into aircraft carriers, with Furious again differing from her half-sisters by initially being flush-decked and later by having a much smaller island.

Another example is the American Essex-class aircraft carriers of the Second World War that came in "long-hull" and "short-hull" versions.

The generally accepted commercial distinctions of a "sister ship" are the following: The critical overriding criterion is having the same hull design.