William was appointed as Ensign of the Porirua Rifle Volunteers in November 1868 and promoted to Lieutenant the following January. The Evening Post of 20 Dec 1869 notified that he "resigned his Lieutenancy in the Wellington Militia."

Two correspondence files are held at Archives NZ Wellington.
[1] Letter from Lieutenant Colonel Reader, Wellington dated 17 Nov 1869 with regard to the resignation of Lieutenant Broderick Wellington Militia

[2] Letter from the Officer Commanding, Wellington dated 24 Mar 1871 forwarding the resignation of Mr W. Broderick as Ensign Porirua Rifle Volunteers