Blue, a white saltire, in the center a white disk with a blue D. (D for Dodero, I assume.)
(There is) a variant, per saltire blue (left and right triangles) and white (upper and lower triangles), a white blue-rimmed oval in the centre bearing a red 'D'.
Compañía Argentina de Navegación Dodero. This appears to be a post WW2 successor to Compañia Argentina de Navegación Mihanovich Ltda. with a connection with their managers Agencia Maritima Dodero S.A. According to one source they were nationalized 29.7.1957 with a change of name to Flota Argentina de Navegacion de Ultramar but their name still shows briefly in Lloyds in the early 1960s for ownership of 1 vessel and this may explain the flag shown here as earlier sources of Talbot-Booth 1949 and Stewart 1953 show a diagonal quartered flag of white and blue with overall a white horizontal oval, outlined blue, bearing a red "D"