He served in
Dublin with the
Worcestershire Regiment between 1919 and 1922, inadvertently capturing
Éamon de Valera in 1921. He was appointed
MBE for his services in Ireland. He then entered the colonial administrative service following two tours of Uganda with the 4th
King's African Rifles, returning there in 1929 as an assistant district commissioner. He moved to
Mauritius as director of labour in 1939, and on his own initiative launched a secret operation to monitor enemy signals. At first he was working on Vichy French signals from
Madagascar and
Réunion, with the help of a growing number of assistants recruited on Mauritius. Amongst them were his sister-in-law, Evelyn DuBuisson (1895-1983), who arrived in Mauritius in 1939 for a summer holiday and stayed for most of the war, having discovered that she had a talent for codebreaking. At first Twining's operation focused on traffic in European languages, but once Britain had declared war on Japan following the attacks on
Pearl Harbor and
Malaya in December 1941, he and his team began working on Japanese signals. Owing to Mauritius' position in the
Indian Ocean and the high altitude of the wireless intercept station on Mauritius, he was able to intercept signals that could not be intercepted elsewhere and he and his team learnt enough Japanese to be able to translate Japanese wireless traffic sent
en clair. The value of the intercept station he ran on Mauritius was recognised by the Royal Navy and by
Bletchley Park, and in order to enhance the capability of Twining's operation three of the graduates of the secret Bedford Japanese School run by Captain
Oswald Tuck RN were sent out to Mauritius: they were trained not only in Japanese but also in codebreaking. Twining's operation was extraordinarily successful but it remained secret until long after the end of the war and he omitted any mention of it from his draft autobiography. In 1943 he became administrator in St Lucia; he was appointed Companion of the
Order of St Michael and St George in the same year. ==Colonial service: Imperial governor==