Peter enlisted with the British Army's Parachute Regiment in Aberdeen in 1960 at the age of 17. After basic training at the Parachute Regiment's Aldershot depot, he was assigned to the 1st Battalion, Parachute Regiment's mortar platoon.

In 1962 Peter transferred to 'D' Squadron, 22 SAS, where he served with the squadron's Mobility troop in Aden. After a few months he was Returned to Unit from the SAS for disciplinary reasons, re-joining 1 Para, where he was posted to Bahrain and Cyprus in 1962–64.

In 1964 he re-joined the SAS and served with 'D' Squadron's 16 (Air) Troop in Borneo and in the Aden Emergency.

In 1968 he was again returned to the Parachute Regiment by the SAS for disciplinary offences related to violent disorder, re-joining 1 Para, which he served with from 1968 to 1969 as a sergeant-instructor.

In 1969 Peter resigned from the British Army. Peter was involved in the Hilton Assignment project, being recruited by James Kent and David Sterling of Watchguard, as team leader. This was an attempt to overthrow Colonel Gaddafi, by raiding one of his prisons in Libya and releasing a large group of political prisoners who would then join in with an already in progress coup. However it was stopped by the American CIA after they applied pressure to the Italian and British Governments. At that time it was thought that Gaddafi was anti communist and would be friendly to the west. How wrong they were. In the 1970s Peter left the United Kingdom for Africa, where he was a mercenary soldier in the Angolan Civil War for several months in 1976, fighting for the National Liberation Front of Angola, assuming command of the formation after the capture of Costas Georgiou.

In early 1977 he went to Rhodesia where he enlisted with the Rhodesian Special Air Service Regiment, being assigned to its 'A' Squadron, fighting in the Rhodesian Bush War with the rank of a non-commissioned officer. In 1979 he joined the British South Africa Police's Special Branch operating in South Rhodesia. After the fall of Rhodesia in 1980, he enlisted with the South African Defence Force's 44 Parachute Brigade, which he served as a Colour Sergeant in the early 1980s, where he assisted with the creation of a new pathfinder reconnaissance unit and took part in the South African Border War.

In 1989 a team of British mercenaries, led by Peter travelled to the criminal empire of the world's most dangerous man in order to assassinate him (Pablo Escobar). The operation was known as Operation Phoenix. The attack plan involved two helicopters flying into the compound at Hacienda Napoles as the mercenaries shot their way through Escobar's massive security operation to kill the drug lord, bringing back his head as a trophy.

When they heard from an informant that Escobar was at his ranch they set off for the target. But the attack was never to happen.

The helicopter carrying McAleese and Tomkins crashed as it flew low through the clouds over the Andes, killing the pilot. The events were told in the 2021 documentary film ‘Killing Escobar’.

In later life Peter became an author publishing 2 books "No Mean Soldier" and "McAleese's Fighting Manual".

Peter is available for media and events, please make contact using the contact us page.