Data frame giving the number of damage incidents and aggregate months of service by ship type, year of construction, and period of operation.
shipstypetype: "A" to "E".
yearyear of construction: 1960--64, 65--69, 70--74, 75--79
(coded as "60", "65", "70", "75").
periodperiod of operation : 1960--74, 75--79.
serviceaggregate months of service.
incidentsnumber of damage incidents.