The 1st Battalion sailed from Malta, and arrived at the Cape about 20th March 1900. Along with the 1st Derbyshire, 1st Cameron Highlanders, and the City Imperial Volunteers, they formed the 21st Brigade, which was created after the occupation of Bloemfontein, the brigadier being Bruce Hamilton, who at the commencement of the war was a major in the East Yorkshire Regiment, and had been in Natal as AAG in General Clery's division. The brigade was certainly most fortunate in its commander, although it was a surprise to many to see one so young get the post. That the selection was right was proved, for no man in the whole campaign did more consistently brilliant work. His record is faultless. He was equally successful as an infantry brigadier and as commander of a number of mobile columns harassing the enemy and capturing laager after laager in the Eastern Transvaal, where he was so long pitted against Louis Botha.
The brigade was ordered to join Ian Hamilton, who was to command the army of the left flank in the northern advance. It may be well to repeat here the composition of his force — namely, the 21st Brigade: the 19th Brigade, under Smith-Dorrien, consisting of the Cornwall Light Infantry, Shropshire Light Infantry, 1st Gordons, and the Canadian Regiment; Mounted Infantry under Brigadier General Ridley; 2nd Mounted Infantry Corps, De Lisle; 5th, Dawson; 6th, Legge; 7th, Bainbridge; Broadwood's 2nd Cavalry Brigade — Household Cavalry, 10th Hussars, 12th Lancers; P and Q Batteries RHA; 81st, 82nd, and afterwards 76th Batteries RFA; Massey's section 5-inch guns,—roughly 11,000 men.
The 21st Brigade joined Ian Hamilton on 2nd May 1900. The work of his force generally is sketched under the Duke of Cornwall's Light Infantry.
At the battle of Doornkop or Florida, 29th May (see 1st Gordons), the Sussex had 5 killed and 15 wounded.
After the capture of Pretoria Ian Hamilton's Infantry Division was broken up, Smith-Dorrien's brigade being needed on the line between Kroonstad and the capital; the 21st, however, remained under the two Hamiltons, and at Diamond Hill had the most prolonged fighting they had seen. The successes of De Wet and the Free State Boers against the lines of communication had encouraged the Transvaalers to close in on the east of Pretoria, and it became necessary to drive them off. On 11th June the position roughly was—French with two Cavalry Brigades, or what was left of them, was on the left; Pole-Carew with the Guards and Stephenson's 18th Brigade in the centre and left centre; the 21st Brigade on the right centre; and Broadwood's and Gordon's cavalry brigades on the right. The position could not be turned, and the mounted men could no more than hold their ground. Mr Churchill in his excellent account of the battle says: "Ian Hamilton directed Bruce Hamilton to advance with the 21st Brigade. This officer, bold both as a man and as a general, immediately set his battalions in motion. The enemy occupied a long scrub-covered rocky ridge below the main line of hills, and were in considerable force. Both batteries of artillery and the two 5-inch guns came into action about two o'clock. The Sussex Regiment, moving forward, established themselves on the northern end of the ridge, which was well prepared by shelling; and while the City Imperial Volunteers and some parts of the mounted Infantry, including the corps of guides, held them in front, gradually pressed them out of it by rolling up their right. There is no doubt that our infantry have profited by the lessons of this war. The widely extended lines of skirmishers moving forward, almost invisible against the brown grass of the plain, and taking advantage of every scrap of cover, presented no target to the Boer fire. And once they had gained the right of the ridge it was very difficult for the enemy to remain. Accordingly at 3.30 the Boers in twenties and thirties began to abandon their position. Before they could reach the main hill, however, they had to cross a patch of open ground, and in so doing they were exposed to a heavy rifle-fire at 1200 yards from the troops who were holding the front".
On the 12th the action was renewed, the Guards supporting the 21st brigade. The Derbyshire advanced on the right, the City Imperial Volunteers in the centre, and the Sussex on the left. Progress was slow, as the enemy's position was very strong, but the 82nd Battery, having been hauled on to the plateau where our troops were lying in extended order, by its splendid devotion maintained the ground won, beat down the Boer fire, and saved a withdrawal; but, as usual when a regiment or battery does a fine feat, the toll had to be paid. Mr Churchill says: "But the battery which had reduced the fire, by keeping the enemy's heads down, drew most of what was left on themselves. Ten horses were shot in the moment of unlimbering, and during the two hours they remained in action, in spite of the protection afforded by the guns and waggons, a quarter of the gunners were hit. Nevertheless the remainder continued to serve their pieces with machine-like precision, and displayed a composure and devotion which won them the unstinted admiration of all who saw the action". In the afternoon two other batteries and more troops were pushed to the front, and that part of the position was carried. During the night the enemy withdrew entirely. All accounts of the battle praise unstintingly the work of the 21st Brigade. Lord Roberts says: "The troops advanced under artillery fire from both flanks, as well as heavy infantry fire from the hill itself. The steadiness with which the long lines moved forward, neither faltering nor hurrying, although dust from bullets and smoke from bursting shells hung thick about them, satisfied me that nothing could withstand their assault. The position was carried at 2 pm ... Fighting continued till dusk, the Boers having rapidly taken up a fresh position near the railway".
No sooner was Diamond Hill over than Ian Hamilton, with, among other troops, the 21st Brigade, was despatched to the north-east of the Free State against the Boers there who were damaging the lines of communications. The general met with an accident near Heidelberg, breaking his collar-bone, and his place was taken by Sir A Hunter.
About 8th July Reitz was reached, where the 21st Brigade were to remain a few days. Thereafter a series of rather complicated movements (detailed in Sir A Hunter's despatch of 4th August 1900) took place, with the object of getting possession of the doors leading into the Brandwater basin and locking the enemy in. On the 16th July the Sussex occupied Meyer's Kop, ten miles west of Bethlehem. On the 20th and 21st Bruce Hamilton had the Camerons heavily engaged at Spitz Kop, but the position was gained. On the 23rd the Sussex had a task which was found rather too heavy, but with the assistance of other troops the objective was gained next day. For some days further Bruce Hamilton had fighting, marching, and stiff hill-climbing, but the result of the operations was worthy of the loss and labour, 1300 of the enemy surrendering on the 30th to Bruce Hamilton, and a large number to other generals,— about 4000 in all.
About 4th July the City Imperial Volunteers had gone as escort to a convoy to Heilbron, where they remained till the 25th. After that they left Heilbron, and were moved to the Johannesburg - Krugersdorp district. They were not again with the 21st Brigade. After 31st July the doings of the brigade are not easily followed. It may be said to have been broken up, although General Bruce Hamilton had the Sussex and Camerons, along with the 2nd Bedfordshire and other troops, in a column which operated in the Kroonstad district during the autumn of 1900.
Twelve officers and 16 non-commissioned officers and men were mentioned in Lord Roberts' final despatch.
Early in 1901 Colonel du Moulin was put in command of a small column, including his own battalion. During the remainder of the campaign this column operated in the Orange River Colony, chiefly to the west of the Bloemfontein railway.
On 28th January 1902 the column was bivouacked behind a small kopje on the south of the Riet, near Abraham's Kraal. At 1 am the picquet holding the kopje was rushed. Colonel du Moulin as he hurried out to repel the enemy was killed, but Major Gilbert taking command, the kopje was recaptured and successfully held against a second attack. The Sussex lost, in addition to their colonel, 10 men killed and 6 wounded. Speaking of the colonel's death, Lord Kitchener used the words, "Whose loss to the army as a leader of promise I greatly deplore".
At one period of the war, when mounted men were much in demand, the colonel of the Sussex got his whole battalion on horseback (see the evidence of General C E Knox before War Commission).
During the latter phase of the war 1 officer and 5 non-commissioned officers and men gained mention in despatches by Lord Kitchener, and in his final despatch 6 officers and 4 non-commissioned officers were mentioned.