"Home waters" refers to the water around Japan. I was just there at that time with the same message about the convoys. I missed finding the first 2 but lucked into the last one, 5 unescorted merchants that found their way to the bottom of the ocean.
About 12 hours later a escort carrier followed them to the bottom.
(hint: look to the NW of Truk and wait past the due date of 18 Dec.)