An officer in the Royal Artillery who eventually rose to the rank of brigadier, he was responsible for developing many of aspects of the commando concept.

[2][nb 1] His family had a strong military tradition, his own father had been a regular officer who had been killed on 14 September 1914 while serving with the 2nd Battalion, Royal Sussex Regiment in France during the First World War.

[4] As he grew up he professed a desire to move to Argentina and breed horses, having heard anecdotes of life in South America from people who lived in his village.

His mother, however, continued to push him towards a career in the army, hoping that he would follow in his father's footsteps and join the Royal Sussex Regiment.

[4] In the end she managed to convince him that a military career was the best option for him given the limited financial resources available to him with which to pursue his business interests.

[10] Initially his unit was the only one in the area and for a time it seemed that there was a possibility for some action, however, they were soon reinforced by other batteries and Durnford-Slater began to think about pursuing other options within the service.

[2][13][14] His appointment came through on 28 June and based in Plymouth, he immediately began the process of recruiting officers for the new unit, drawing personnel from the Southern Command region.

[15] Within a fortnight Durnford-Slater led a group of 40 men from the unit's 'H' Troop on a probing raid on the German-occupied island of Guernsey, as part of Operation Ambassador.

[16] The raid was largely unsuccessful, and indeed momentarily threatened to derail the further employment of the Commandos,[12][17] however, the lessons learnt from the operation did help in the development of many aspects of the concept which Durnford-Slater set about implementing almost immediately.

[27] The recommendation, written by Haydon, credits Durnford-Slater's "personal courage, complete coolness & quick grasp of the situation" with inspiring the confidence of the men and ensuring all objectives were achieved.

[28] It further describes how, when the attack was in danger of stalling, after the leading troops "lost five out of six officers, & nearly 40% of their effective [strength]" he took personal command to restore the situation, and under heavy fire had both his orderlies wounded beside him.

Many of the landing craft had either been sunk or damaged and forced to return to Newhaven, while Durnford-Slater himself spent the rest of the day watching helplessly from one of the ships as the battle proceeded without him.

[29][nb 3] A period of lull followed for Durnford-Slater and his men which enabled him to rebuild the unit after the losses they had suffered at Dieppe.

3 Commando's assault on an Italian battery north-west of Cassibile on 10 July 1943,[32] before launching another seaborne assault on 13–15 July, this time around Agnone, to capture the Ponte dei Malati, a bridge spanning the Leonardo River to the north of Lentini and 10 miles (16 km) behind the front line as part of the advance on Catania.

[34] The recommendation describes how they had to hold the bridge for 18 hours until relief arrived, in the face of German counterattacks supported by tanks and heavy mortars.

In early October he led the detachment in Operation Devon, where they were employed to spearhead the assault on Termoli, on the east coast of Italy, about 120 miles north of Bari.

[40] The town was taken despite intelligence failures, it was expected that they would face only administrative units of the German 1st Parachute Division, but in fact 26th Panzer Division were in the area, being rested following the fighting at Salerno; and problems during the landing, some landing craft of 40 Commando and the SRS grounding fifty yards offshore in six feet of water, leading to the loss of all their radios as the men waded ashore.

[42] In November 1943, a divisional-sized headquarters unit, known as the Special Service Group took command of all Allied commando forces, which at the time included four independent brigades spread throughout the United Kingdom, Italy and the Far East,[43] and upon his arrival in London, Durnford-Slater was promoted to brigadier and became deputy commander underneath Major General Robert Sturges, Royal Marines.

[47] For the rest of the war, he alternated between time at the front in France and then Germany and in the United Kingdom, carrying out varied administration, logistics and planning tasks.