On the suppression of the mutiny he was appointed orderly officer at Addiscombe Military College, a post which he occupied till the closing of that institution in 1861, when he retired from the army with the rank of captain.
[1] In 1866, Armstrong took up the duties of secretary and registration agent to the Westminster Conservative Association, and his efforts were largely responsible for the electoral defeat of John Stuart Mill by W. H. Smith in November 1868.
The paper was losing money, but Armstrong, without previous experience of journalism, transformed it into a valuable property, and made it an influential supporter of Benjamin Disraeli in the London press.
The Globe was made over to him by the owners in 1875, and in 1882 he acquired a major interest in The People, a Sunday conservative paper with a large circulation.
A summary of that document had been brought to the paper by an occasional contributor, Charles Marvin, to whom the foreign office had given employment as an emergency "writer".