I have checked the Seikai Maru like follows.
Ref code: B10074880000
@JACAR
Dated July 10, 1937
Regarding the search of (Ms) Earhart
To Consulate General Fukuma in Honolulu
From Foreign Minister Hirota (Tokyo)
"In answer of your question No.174, we are sending the Seikai Maru to the Marshall Islands and the special-service ship Koshu toward the estimated flight route of the Earhart plane but no clues at the moment. They will begin search upon arrived at Jaluit on/around July 12....."
Ref code: B10074880000
@JACAR
Dated July 10, 1937
Regarding the search of (Ms) Earhart
To Consulate General Fukuma in Honolulu
From Foreign Minister Hirota (Tokyo)
"In answer of your question No.174, we are sending the Seikai Maru to the Marshall Islands and the special-service ship Koshu toward the estimated flight route of the Earhart plane but no clues at the moment. They will begin search upon arrived at Jaluit on/around July 12....."