In April 1864, Beale was commissioned as an assistant surgeon in the 4th Regiment of the Waikato Militia, which was actively engaged in the Invasion of the Waikato. He initially worked in Auckland's outlying villages of Howick, New Zealand and Onehunga but by March 1865 was based in Hamilton, on the banks of the Waikato River. Soon afterwards, he received a land grant in the town as part of his payoff for serving with the Waikato Militia.