Educated at Eton and Sandhurst, he was commissioned into the King’s Royal Rifle Corps (60th Rifles) in 1929 and served with the 1st Battalion at Lucknow and then in Calcutta at the time of the major earthquake in East Bengal. He was adjutant of the battalion in prewar Burma, where the military priorities centred on polo and shooting duck, but he took his profession unusually seriously for a young officer of the period.

In England with the 2nd/60th Rifles on the outbreak of war, he served briefly at the Winchester depot, training recruits, before attending the wartime course at the Staff College, Camberley. Early in 1941 he became Brigade Major (chief of staff) to the 38th (Irish) Brigade based in Norfolk. Together with other formations which were to comprise the British 1st Army, 38th Brigade was training hard for the Allied invasion of French North Africa — Operation Torch — which took place in November 1942.

He was Brigade Major of 38th Brigade throughout the difficult battles of the 1st Army’s advance on Tunis and then in the invasion of Sicily in July 1943. After the successful conclusion of the campaign in Sicily, he was appointed MBE and, soon afterwards, promoted acting lieutenant-colonel to take command of the 5th Reconnaissance Regiment in the 5th Infantry Division.

The Reconnaissance Corps was raised during the war to provide infantry divisions fighting in Europe with a fast- moving reconnaissance capability using robust, cross-country armoured cars with the firepower necessary to fight for the information they sought. The 5th Reconnaissance Regiment had been formed from a Territorial Army battalion of the Rifle Brigade, so Douglas-Pennant felt at home immediately with London riflemen such as served in his own regiment.

In the last week of May 1944, the 5th Recce Regiment took part in the break- out of the 5th Division from the northern sector of the Anzio bridgehead. This was a diversionary action to allow the US VI Corps to mount the main offensive towards Highway 6 and cut the road to Rome. But after reaching the mouth of the Tiber south of the capital, Douglas-Pennant later led his regiment into a warmly welcoming city.

An unexpected interlude followed. For six months the 5th Division was pulled out of Italy and sent to Palestine, ostensibly for rest and retraining but also to keep an eye on the internal security situation there. Returned to Italy at the end of 1944 with his regiment, he was abruptly ordered to take it to Naples for shipment to Marseilles and from there by train to join the rest of the 5th Division, which was on its way to join the British Second Army in northwest Europe.

This tortuous journey was accomplished with some sweat and difficulties, but the regiment arrived in time to take part in the Second Army’s advance into Germany, eventually reaching the Elbe. After the end of the war in Europe, Douglas-Pennant was awarded the DSO for his skill and determination in command of the 5th Reconnaissance Regiment.

He stayed on in Germany as a staff officer until 1948 when, reverting to his substantive rank of major, he joined 2nd/60th Rifles as second in command. At the time, 2nd/60th was the training unit for the regular 60th and Rifle Brigade battalions, but three years later, when the shortage of infantry to meet operational demands abroad called for the battalion to resume a full active role, he was appointed to command.

It was no ordinary commitment. The battalion was made up half of 60th Rifles and half of Rifle Brigade and, although they had a long and close association, the two regiments were so different that there were many who said the mixture would never work. That it worked particularly well was due to Douglas-Pennant’s personality, combined with his insistence on the very highest standards of shooting, which pushed petty differences aside and won the Bisley rifle match.

He was an ideal choice to command a hastily-formed unit facing a demanding programme of training as a motor battalion to join the Army of the Rhine in the spring of 1952. Not only was his wartime experience invaluable in this role but he also had the priceless gift of self-confidence that permits no bullying by senior commanders or the staff. He always backed his subordinates, even when they were in trouble.

After completing command of 2nd/60th in Germany, he commanded the Rifle Depot in Winchester until he was made Brigade Colonel of the 60th and Rifle Brigade regular and Territorial battalions, through to his retirement in 1958. While in Germany, he met and six months later married Elizabeth (Betty), daughter of Brigadier Sir Percy Laurie of Bletchley, Buckinghamshire.

The Honourable Malcolm Frank Douglas-Pennant was the second son of the 5th Baron. The Douglas element of the family stems from William of Douglas, who lived in the Scottish borders at the turn of the 12th century, while the Pennant side is descended from Richard Pennant (1737-1808), the first and only Baron Penrhyn of Penrhyn. The surname Douglas-Pennant is therefore more in recognition of Pennant inheritances in Wales than of Welsh ancestors. In 1951 Penrhyn Castle and associated lands were transferred to the National Trust in lieu of death duty.

He inherited the title in 1967, his elder brother, Admiral the Honourable Sir Cyril Douglas-Pennant, having died without male issue. He lived and worked on Dean Farm in Hampshire until he moved to Littleton Manor in 1980. He was a dedicated nature conservationist. He was also closely involved in planning and fundraising for the Wessex Nuffield Hospital near Winchester.

He is survived by his wife and two daughters. The title passes to his nephew Simon Douglas-Pennant.

Colonel The Lord Penrhyn, DSO, MBE, 6th Baron, was born on July 11, 1908. He died on November 8, 2003, aged 95.