You may be aware that 28th Maori Battalion in WW2 was divided into companies that reflected tribal links.
'The battalion was to be organised on a tribal basis, and to this end men from North Auckland (the Ngāpuhi and subtribes) were marched into A Company lines; B Company received the men from Rotorua, Bay of Plenty, Taupo, and the Thames–Coromandel areas, mostly from the Arawa confederation and Tuhoe tribes; C Company comprised the tribes of the East Coast from south of Gisborne to the East Cape, Ngātiporou, Rongowhakaata, and sub-tribes; D Company, unlike the others, which were from compact areas with a closely-knit tribal organisation, extended from the Waikato–Maniapoto confederation area south of Auckland and included the Taranaki tribes, the Ngāti Kahungunu of Hawke's Bay–Wairarapa, the Wellington Province, the whole of the South Island, the Chathams and Stewart Island, and odd men from the Pacific Islands."
https://nzhistory.govt.nz/war/maori-in-second-world-war/response
You say he went by several names....Matene is the transliteration of the surname Martin so it is not really a different name. Are there others you know of? Do you think another name may have Tahu in it
There is a great resource for Maori land here
https://www.maorilandonline.govt.nz/gis/owner/interestSearch.htm
There is a Wairongoa Matene holding land in the Taitokerau rohe. Te Hapua 41. if this your family's kin then the land is way way up north and so if he served in WW2 it is likely that he served in A Company of 28th Maori Battalion.
If he was born in 1900 he would have been very young but it was not unknown for young men to put their ages up. My own uncle ran away to Australia and joined the AIF saying he was 18 when he was barely 16.
In WW1 the units were known as the Pioneer Battalion.
If you scroll down in this link you will see some of the hat badges.
https://nzhistory.govt.nz/war/maori-and-pacific-units/maori-units
The other idea I had was that he may have gone to a secondary school where he joined cadets or whatever they would have been called and this might have been their uniform.
His shoulders & collar seem to be free of any badges etc (from what I can see) EDIT.
I do have a sort of personal connection to a Martin family (part of my ex husband's family). They were from around Waitangi so south of Te Hapua and there was a Maclennan link from Awarua, Fortrose, Catlins area.
Edit I looked on the Maori land online site under Tahu Wairongoa (actually Tahu Wairongoa Matene) and it has come up with another reference to a block of land
https://www.maorilandonline.govt.nz/gis/title/30072.htm
Parengarenga B3A Recreation reserve. Also Taitokerau.
This is in the same general area as Te Hapua.
You can carefully read the online file and you may be able to find out a bit more by writing to the Registrar. They may be able to search the 'succession orders or the history of the block to see who he succedded to his share fom and who succeeded to it....if anyone has?
Finally Nga Puhi has roll lists and help is available for those who want to whakapapa back to a Nga Puhi ancestor.
Thank you very much for your helpful and informative reply. I was not aware that the 28th Maori Battalion were divided into companies in such a way, and given that he was from Northland, as was his father, Matene Tahu, I would assume he would be in A Company.
I've attached a screenshot with other names (transliterations) that I've encountered him using in various records, and going by this, the entries you found in the Maori Land Records are most likely him. I did find 2 electoral rolls for whom I believe is his father, Matene Tahu, and on this his Iwi is recorded as being Te Aupouri, so I would assume that William was also of that Iwi. However, one of his wives, my children's ancestor, Te Kopa Peka, was Ngati Hine, which once was considered a sub tribe of Ngapuhi. I have also been told by my children's Uncle that William was Te Aupouri, but other than that, he hasn't proved to be particularly helpful in my search.
I'll definitely take a look at those hat badges, and see if there is one that resembles William's. Regarding Te Hapua 41, I've encountered that before but can't find out where from as am staying away from home at the moment and don't have access to the PC where I keep my research on, just my Ancestry tree.
Thanks again, and if any of the information I've provided aids you further in regard to more information, it would be greatly appreciated