Successive S138 batches changed from four coal-fired boilers to three coal-fired boilers and one oil-fired boiler. Propulsion also shifted from two-shaft triple-expansion machinery to turbines on two and then three shafts. Nominal top speeds of roughly 30-32 knots concealed differences in how well the boats maintained speed on trials. Turbine boats performed better in this respect than some of the reciprocating-engine boats. Those differences raised doubts about maneuvering the earliest and latest batches together, even though they shared a class designation.
Notable Point · 40:54-42:22
Different S138 machinery complicated flotilla maneuvers
Early and late S138 batches differed in machinery and sustained speed, complicating their use together in formation.