Educated at Sir Walter St John's Grammar School For Boys, Janes was commissioned into the Royal Artillery in 1942 during World War II. He was appointed Commander, Royal Artillery in 1965, Deputy Military Secretary in 1967 and General Officer Commanding 5th Division in 1970 before becoming Director Royal Artillery in 1971. As Director Royal Artillery he visited Oman during the closing stages of the operation to remove communist forces following the Dhofar Rebellion. He retired in 1973.