My understanding is there wasn't a Royal New Zealand Navy Flag in WW2.
New Zealand, Canada and Australia all used the White Ensign until well into the 1960's. Indeed when WW2 started the Royal New Zealand Navy didn't even exist. It was The New Zealand Division of the Royal Navy. So if you're being pedantic at the Battle of the river Plate it was HMS Achilles not HMNZS Achilles. Having said that I don't think anyone objects to her being called HMNZS and it wouldn't be wise to mention it in front of her crew!
You might want to ask this question on Britmodeller. Given our common heritage it's a good place to find Kiwi Navy modellers hanging out.
Terry
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