Im no defense analyst , but it makes perfect sense to me, and i cant see that the implementation would be overly difficult.
Remain Kiwi (whatever that entails ) but be part of a joint defense force . I dont see the need to be completely absorbed into Australia, just contribute to their/our defense budget .
Im sure there are a zillion of reasons why it wouldn't work , but i bet there are more reasons why it would (work)
The Australasian Defense Force ....... sounds good, now come up with an appropriate badge and roundel .......or , tell me why it wouldn't, or shouldn't happen.
On an aside, soon , we may no longer need a passport to travel to the land of Oz....... if we can get that close, then why not consider the merge, its not rocket science,,,,or maybe it is
