Why sister ships can finish a war in different mechanical condition

Why might one sister ship be unable to move at the end of a war while another remains mobile?

Different damage, maintenance, machinery wear, and individually fitted engine components can leave sister ships in very different condition.

Different maintenance histories, accumulated damage, and wear can leave sister ships with sharply different mobility. Large marine engines are produced in small numbers, so even machinery described as mass-produced can involve components selected and adjusted for an individual installation. The discussion compares production in tens of large engines with some later turbine or diesel families reaching hundreds over a long period. Successive batches can involve different workers and repeated design revisions. A shared class specification consequently does not guarantee identical mechanical condition at the end of a war.