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The service history of a naval destroyer, HMCS IROQUOIS, was analyzed to develop an operational profile for structural fatigue assessment. The data from 1972 through 2012 provides insights for developing data sample requirements and wave data collection approaches applicable to other aging vessels. The results show that capturing daily wave data at the recorded position sufficiently describes the encountered seaways. Artificially reducing the data set to represent incomplete hull monitoring or operational data indicates that 5–9 years of wave data were required to limit the damage rate coefficient of variation to within 15%. However, operational changes, such as those observed after this destroyer’s midlife refit, may increase data requirements. Similar requirements for convergence were observed in duration-at-sea data derived from annual days at sea or distance sailed. The findings, consistent across the class and another class of ships, show that results for this ship are not anomalous.