Map reference system - South West Pacific Area

[Baska]

In a P-38 crash (or ditching) I am researching, I came across the use of a map reference that is unknown to me. I know this particular P-38 came down near Jefman aerodrome (Japanese drome near Sorong, West Papua, Dutch New Guinea) on September 5th 1944. The pilot, Lt Charles W. Springer, was rescued from the ocean by an 2 Emergency Rescue Squadron Catalina.
The map reference used is 61 Olson 45

Any ideas what this reference could be?

This is a 1944 map of the area:

 

[NTGray]

I was unable to find anything with Google that would answer your question. However, it does seem obvious that the code was so that if the Japanese intercepted the message they would not be able to get to the downed pilot first and capture him. There may have been a standard system in general use, or the code could have been revised every morning in that region. I'm guessing that a good direction to go would be to find some historical records about PBY rescue squadrons and see if they contain any useful information.

 

[Baska]

Good suggestion! I'm in touch with Jim Teegarden of 2nd Emergency Rescue Squadron (2ERS) and he might know this reference grid system.

 

[FLYBOYJ]

As mentioned I think what you're looking at is a "gridded" map and the location may be based on the numbers shown vertically and horizontally with a code thrown in. Many years ago I did SAR work with the Civil Air Patrol and we used a gridded map and would send locations in a code to avoid other aircraft coming into our search area, especially local news media.