Recently found this is someone's backyard, sitting in the dirt. No idea where it came from, why or how long it was sitting there.
All I know is that it is British / Commonwealth style helmet. The helmet is in Australia. There are no marking on it that I can see. There are two fixture points on the sides and one on the top.
There is an entry hole at the front, but I have no idea if that is combat related or if someone just knocked it in with a hammer. There is also a hairline crack off to the left of it.
Here are some pictures: