A sister ship is a ship of the same class as, or of virtually identical design to, another ship. Such vessels share a near-identical hull and superstructure layout, similar displacement, and roughly comparable features and equipment. Often, sisters become more differentiated during their service as their equipment (in the case of military ships, t...
[n] - a ship that is one of two or more similar ships built at the same time
noun a ship that is one of two or more similar ships built at the same time