MACR were designed to cover a loss occuring in an aircraft (with notions of aircraft serial, take off hour and so on). AFAIK only the one referred above was for a loss not involving an aircraft. There are several MACRs for RAF Bomber Command aircraft having an American crew.
But MACR does not cover all missing aircrew. If an aircraft was based in the USA and went missing during a patrol or a training sortie, no MACR was issued.
As for losses occurring at sea, you can check US Navy war diaries available on fold3 if you have a pay account. Or you can check the IPDF for each casualty.
All USAAF personnel lost in WWII are supposed to be listed in the database available at
http://www.usaafdata.com/search. I have found some men to be missing but would say that over 95% of the USAAF deaths, including in the USA, in ground incidents or in ship sinkings, were there in the case I studied. You can try to type the name of your ship in the details field with the "contain" search option. It works well for the Dorchester and the Paul Hamilton. On the other hand the troopships Cape San Juan sunk in November 1943 with USAAF troops aboard is not listed. Most of the casualties were from 855th Engineer Battalion -Aviation, and typing "855th" in details give you 13 casualties for 11 November 1943, while ABMC has 98 for the same day. Most of the USAAF casualties aboard Cape San Juan are missing in the
http://www.usaafdata.com/search database, the biggest missing number I have met so far using it.
Best it to search with the airman name still, as many entries are lacking for a details field (or show only BG or FG).