We analyse 635 set-years of service experience of 147 merchant-marine steam-turbine-gear propulsion sets, finding an MTBF of 23.5 set-years. The sets of one good-sized fleet have 3 times as large an MTBF as the rest of the sample, a fine return on the more conservative attention paid them.The sample size increased linearly with date. The most satisfactory analysis was as a plot of age-wise cumulatives of failures and service-life. This detected a significant short relatively trouble-free wear-in period with an MTBF of 9.3 set-years; later service had a 27.6 set-year MTBF.We discuss many failure modes and the design and operating practices that minimize them. Much of the favorable MTBF comes from avoiding all but a very little innovation in the design of individual sets.