He returned to the South Africa and back into the Union Defence Force ranks at the end of the war.[4]: 6 He was commissioned and sent to England to train as battery commander as well as attending a staff officers course.[4]: 7 He returned to South Africa in 1922 and was promoted to Adjutant of the South African Field Artillery.[4]: 6 In 1930 he was a Lieutenant-Colonel of 1st Field Service Brigade in Ladysmith.[4]: 6 He commanded Orange Free State Command from 1935 to 1937. Other positions held were Voortrekkerhoogte and Transvaal Commands.[4]: 6 When war started he was promoted to Brigadier.[4]: 6
During the early stages of Operation Crusader, the 5th South African Brigade was destroyed on 23 November 1941 at Sidi Rezegh. This loss is thought to have spurred Pienaar to disobey a series of orders to engage the enemy over the remainder of the battle. Pienaar's 1st South African Brigade was situated 25 miles south of Sidi Rezegh at Taieb El Esem. Over the following week, Pienaar was first ordered to hold position at Taieb El Esem and later to move north to relieve the encircled 2nd New Zealand Division of XIII Corps. Instead, Pienaar defied his superiors;[9] his brigade withdrew from Taieb El Esem and was then slow to move north to relieve the 2nd New Zealand Division, who were then partly overrun and forced to retreat. Historians have argued these actions qualify as insubordination by Pienaar, who is thought to have been reluctant to commit his troops after the loss of the 5th South African Brigade, fabricating or exaggerating reports of enemy attacks as justification for actions.[10] However, despite incurring the anger of senior commanders at the time, he was not formally disciplined.
On the other hand, Ronald Lewin, who took part in the entire campaign, writes: "what is striking . . . is how often the British would squander a complete armoured brigade in some useless assault on a fixed position."[11] Pienaar simply did not buy into the "Up Guards and at 'em!" approach of the British, which led to the decimation of the Commonwealth and Indian divisions that bore the brunt of so much of the fighting in the Desert War. "You know the three things I hate in this world—British lords, British generals and these bloody Guards!" he told Brigadier E. P. Hartshorn.[12]: 171 regarding the loss of Tobruk in 1942. Churchill wrote in volume 4 of his memoirs, The Hinge of Fate, "The burden of blame falls upon the [British] High Command rather than on [the fortress commander, South African] General [Hendrik] Klopper and still less on his troops."
On 20 November 1942 he was appointed Companion of the Order of the Bath (CB) "in recognition of the supreme gallantry and magnificent achievements of British and Dominion Troops and their Commanders in the present operations in the Middle East".[13]
In 1942, Major General Pienaar was killed in an air crash in Kenya on his way back to South Africa.[14] The plane crash occurred early Saturday morning in Kavirondo Gulf at Lake Victoria killing him and eleven South African officers and men,[15]: 3 including Colonel Frederick Theron, Lt. Col. Eric Vickers Frykberg and Lt. Col. Eric Loftus Mackenzie.[16] The plane crashed 16 km (9.9 mi) from the airfield at Kisumu when a combination of pilot fatigue and an electrical fault in the undercarriage which could not be raised, resulted in a loss of speed and failure to maintain height and it flew into the water.[17]: 3 He was survived by his wife Norma and his children: Nelia, Barry and Fay.[18]: 7
Sam Brewer, war correspondent for the Chicago Tribune, wrote in an obituary that Pienaar was "acknowledged by all the military authorities...as one of the best fighting leaders the British have found in this war. He was every inch a soldier and a man, and on top of that had a quality not always found in a tough general—he was loved like a father by his men. . . . More than once he had hard words with higher authorities when he thought insufficient attention was being paid to the safety and comfort of the footsloggers who were bearing the brunt of the fight. Two points struck everybody who met Dan Pienaar—first his disregard for personal danger; second his solicitude for his men."[12]: 178
