Hi Dave, SG lists these under Japanese Occupation of Netherlands Indies for use in the Japanese Naval Control Area issued in 1943. They are two of a set of 11 in two different designs. Scott lists them as occupation stamps at the end of the Netherlands Indies listings as Scott #N30-31.
Thanks Nigel. I suspected that they were an occupation issue with the Japanese flag superimposed over the tropical beach, but looked at 25 other places than Netherland Indies! Cheers, Dave.
https://colnect.com/en/stamps/list/country/908-Netherlands_Indies_Japanese_Occupation_Naval_Area/year/1943
