In June 1926, Frederick aged 17 joined the British Army as a 'Boy entrant'. He left the army in 1936 but rejoined in 1941. Then he joined the Territorial Army, the 226th Light Anti Aircraft (T) Regiment, Royal Artillery and during this war enlistment was stationed predominently in the UK.

He was awared the Defense Medal and the 1939-45 medal, having already been awarded the India General Serivce Medal in his previous service.
In 1947 he switched to a regular service engagement (as opposed to war service) of 4 years, staying with the Royal Artillery (Heavy Anti Aircraft)
In 1948 we find him in the Isle of Man giving him the oportunity to visit his daughters Diana and Janet.
1950 saw him posted to Gibraltar and also extended his service by another 5 years (to total 9 year regular engagement on top of the 6 in the Teritorial Army).
Whilst on leave he ran into some sheep on his motorbike and suffered a fractured elbow.
Whilst in Gibraltar Frederick remarried (Dorothy Proudfoot)
In 1953, now, Sergeant Alexander was posted back to the UK.
His son, Andrew Keith Alexander was born in 1954 (Liverpool)
1956 saw Frederick posted to Kenya for 5 years and was awarded the General Service Medal with Kenya clasp 
Returned to the UK, in 1962 he extended his service again to a 22 year engagement. 
During his carreer he reached BQMS (Battery Quarter Master Sergeant) rank - equivalent to Staff Sergeant but with additional logistic and administration responsibilities and sometimes held by a warrant officer.
In the final year of his service he served at the Army Outward Bound School in Wales where his superiors stated 'An entirely honest and conscientious man who has had considerable responsibility at this school and has carried it well. Of vey quiet and sober habits well mannered and polite. A pleasant personality and quite good at handling others' 
October 1963 saw him leave the army, as a staff sergeant, and settle in Liverpool. He had a terminal grant of £1,405 6/- and a weekly pension of 180/2 (180 shilings and 2d).
