Kammala wannan jumla: Rundunar Sojan Ruwa ta shiga karkashin umarnin kai tsaye na Babban Ofishin Jakadancin Imperial a 1937. Tare da farawar Yakin Pacific tare da kai hari kan Pearl Harbor wanda "Kido Butai" (1st Air Fleet) na Combined Fleet ya yi, Combined Fleet ya kusan zama daidai da Navy na Imperial Japan, a karkashin umarnin admiral Isoroku Yamamoto har zuwa watan Afrilu 1943 lokacin da ya mutu bayan da sojojin Amurka suka harbe jirginsa a kan tsibirin Bougainville. Ya ƙunshi jiragen ruwa, masu jigilar jiragen sama, jiragen sama, da kuma abubuwan da suka hada da babban karfi na IJN. An fara tattara shi gaba ɗaya don yakin Midway. Bayan mummunar asarar masu jigilar kayayyaki a Midway da kuma a cikin
Yaƙin Solomon Islands, an sake tsara rundunar sojan ruwa zuwa "Area Fleets" da yawa don sarrafa ayyukan gida na yankuna daban-daban. Sa'an nan kuma Ƙungiyar Ƙungiyar ta zama ƙungiya mai gudanarwa.