First off a small correction - "HMS"(His/Her Majesty's Ship) is a prefix used for commissioned (British) Royal Navy ships. "MS" as in "M.S. Sloterdyk" (correct spelling) stand for "Motor Ship" as opposed to "SS" for "Steam Ship". The Sloterdyk remained a Dutch ship under the US War Shipping Administration with a complement of US Navy personnel on board.
It is interesting that your father was (perhaps started off as) an Electricians Mate 2nd Class and attained the rank of Commodore, presumably in the US Navy. The rank was more or less abolished after WW2 and in later years became more of an honorary title. Do you have more information about his naval career?