Mason Elliott joined the Hampshires in 1908 and transferred to the Hampshire Royal Horse Artillery on its formation in 1910. He was commissioned in 1912 and served in Egypt and Palestine throughout the war rising to the rank of major. He was awarded the DSO in 1918. After the war he joined the Hampshire Yeomanry, a unit of the Territorials. Rising to the rank of brigadier, in 1937, he took charge of the 72nd (Hampshire) Anti-Aircraft Brigade a unit of the 35th Anti-Aircraft Brigade (United Kingdom). He remained in command throughout WWII and was awarded a DSO and OBE in recognition of his long and distinguished service.