In Australia. The day was chosen because it's the anniversary of the Battle of Long Tan when 108 members of D Company 6 RAR were attacked by about 2000 VC and NVA regulars in the Long Tan Rubber Plantation in Phuoc Tuy Province. In the course of the battle 18 Australians were killed to (officially) 245 NVA/VC (captured documents by the US latter in the war showed 500 dead). It's basically ignored, because, Vietnam War.
