联合国军
In April 2019 it was announced that Mayer would be appointed Deputy Commander United Nations Command in South Korea later in the year. He relinquished Head Force Design in June and, promoted vice admiral on 18 July, succeeded Lieutenant General Wayne Eyre of the Canadian Army as Deputy Commander on 28 July. He is the second non-American (after Eyre) and first Australian to hold the post in the 69-year history of United Nations Command.