Help ID what this is for.

[Happy Hooligan]

I picked this up at an estate sale this weekend and I'm not sure what this cover was made for?

It's From the Signal Corps and looks to be from 1941.

It's huge, 33" x 34".

and looks like it says 6 F.B.

Any clue?

 

[Silver Surfer]

looks to me to be a mail satchel

 

[Smithy]

Could be a radio or field telephone cover as they came in differing sizes and dimensions depending on the piece of equipment. US field gear isn't really my bag (pardon the pun) but I've seen similar things in the past. Hopefully someone more knowledgeable can weigh in.