The Japan carrier and the planes used HF for comms, of course. The DF request was only sent from the plane if the plane was having trouble with finding way.

BTW was also looking at some article about that lost flight of fighters in a Pacific "routine" transfer flight ( Nanumea comes to mind ) and YE working distances are mentioned. I don't have time right now to read the whole article. I did note with surprise it says the Mayday from one plane was heard by Pearl, and that means: HF. I would have guessed and guessed wrong, the fighter planes were all VHF by now. Oh yeah...the YE range in the article was arrived at by that usual "height of antenna and plane" formula, which in this case i thought unrealistic and way optimistic, something like 165 miles IIRC.