There is a colour video of a USCG PB4Y-1 on Guam colour drated 3 July 1945 (see the final part).This was being used to check the LORAN navigation system
View: https://www.youtube.com/watch?v=WjVZbXVRUsk
There was a large network of LORAN stations in the Pacific in 1945 (72?) all needing checked for accuracy. There was a LORAN station established at Cocos Island on the southern tip of Guam. Constructed from Nov 1944 the network became operational on 1 March 1945 and was manned by the USCG.
An extract from this reads as follows:-
"Coast Guard Plane, PBY-5 no. 189 piloted by Lt. Comdr. Clement Vaughn, the first
plane to be assigned to western Pacific Loran construction work, was still in continuous
use. This plane which carried the siting parties to the various sites, was used in inspection
of the stations, and made many long flights in the running of system accuracy checks on
the completed Loran chains. The conditions under which the plane and crew worked
were, at times, extremely hazardous.
Coast Guard plane, PBY-5A piloted by Lt. (later Lt. Comdr.) O"Neill, was also assigned
to this Loran work. This plane in turn was exchanged at Kaneohe Air Station, Hawaii, for
a Liberator, No. 490, and with the same crew was based at Guam. Later the Liberator was
exchanged at Tinian Air Station for a Privateer, No. 598, which proved even more
valuable in the work, due to greater carrying capacity and higher speed. Over 180
missions and 700 flight hours were performed by this crew. The Privateer was transferred
to DCGO, 14ND, late in December."
So it would appear these airdraft were on temporary loan from the USN, rather than permanent assignment to the USCG.