An article on this website lists the 81 Mathesons (including those with similar names) from New Zealand who I’ve found to have served overseas during the First World War. I’ve now researched those who joined the army but did not leave these shores, and discovered 22 more.
Their story shows an army increasingly desperate for soldiers, conscripting or accepting men who were physically not suitable for active service. Many others were simply not needed as the war came to an end, and were sent home from training camps. The post is here.