While sorting through my military, again (

) I came across this cover and I was wondering if this was a form of U.S. "Black-Out" cancellation?? From what information I have, the U.S.A.P.O. on this cover served engineers based in Oahu, Hawaii (?) The return address clearly states SF, California but the previous owner of this cover, not known to me, pencilled in Oahu. T.H. which I assume is for the Territory of Hawaii?
Any help would be appreciated.
Chimo
Bujutsu
