Triple expansion refers to three stages of steam expansion, not necessarily three cylinders; Titanic, for example, used four cylinders across three stages. The Liberty ships show that even American wartime production had hard limits. United States industry could not supply enough turbines for both the warship program and the immense merchant-building effort. Existing factories could, however, build reliable and highly refined triple-expansion engines in volume. The choice preserved scarce turbine capacity for warships while matching Liberty ships with proven machinery suited to their merchant role.
Notable Point · 37:48-39:19
Why Liberty ships used triple-expansion engines
The Liberty-ship example shows why wartime production capacity and mature machinery could outweigh the superior power of turbines.