






Loughran identifies S553 as the original form, with the flag changing shortly after the Second World War to S554. Rosanoski doubts S555. Merchant Ships 1949 says the flag was unknown. The FOTW S553 rendering places the diamond frame within the field, unlike its cited sources.
A new livery was adopted in 1970 as S556, followed shortly by the S558 funnel. S556’s flag is not supplied by Loughran and was taken from Brown 1978. This sequence leaves S557 unexplained. The FOTW S558 image cites Stewart & Styring 1963, but that source actually shows S557.
The published version follows US Navy’s 1961 source.