FAA Hellcat antenna mast

Hi all,

A simple question linked to some pictures I’ve seen on the web.
Some FAA Hellcat, either in ETO or PTO, has a short kind of antenna mast behind the canopy in place of the standard USN F6F antenna mast.
Why so as not all Fleet Air Arm Hellcats had this feature?
What was the atenna aerials arangement?
Thanks in advance.

Small antenna Hellcat

USN Type antenna mast