Map symbol

[cardboard_killer]

This is from a 1957 document showing the search path of B-24s over the Pacific Ocean in 1944. Does anyone know what the symbol means?

 

 

[Heliopause]

The Tacan system came to my mind. Looked it up. Has a symbol resembling it.

https://en.wikipedia.org/wiki/Tactical_air_navigation_system

 

 

[dbuile]

No idea, but made me wonder if some kind of Sector Search pattern reference (3-lobes, used when searching water by boat).