General Botha was engaged in April and May, 1915, clearing the railway system of the enemy. To prevent any flank attacks it was necessary to hold the two main lines, which run from Swakopmund north to Grootfontein, Tsumeb, and to Windhoek. This line being cleared for fifty miles, Colonel Skinner and the Kimberley Regiment were stationed at Trekopje, which became the Union railhead.
On April 26, 1915, about 700 Germans and a dozen guns vigorously assailed this encampment and for four hours the fight raged with varying consequences. The Germans under a withering fire from their batteries tried to surround the Union trenches to enfilade them, but were forced to retire, when they had got within 150 feet of their objective, leaving twenty-five killed and wounded behind them. The Union force lost eleven men, of whom three were officers, and forty wounded.
Meanwhile, the southern army was actively engaged. Sir Duncan Mackenzie's column had dispersed the Germans and taken some booty from one or two places near Lüderitz Bay, and had seized many miles of railway. On February 22, 1915, his advance guard occupied Garub, a station seventy miles inland. Here a company of Union scouts pushed after the retiring Germans, and in a skirmish with mounted men protecting a troop train their leader was wounded. They were forced to retire, leaving one of their comrades a prisoner in the hands of the enemy. The British camp at Garub was also attacked by a hostile aeroplane which dropped hand grenades and shells, but there were no casualties.
Aus, an important station fifteen miles from Garub, was next occupied by Mackenzie. The place was evacuated without a struggle, but it showed that much work had been done to fortify it, and that the enemy had intended to resist. Owing to the rapid movements of the British force the Germans had abandoned everything, though several mines exploded when the town was occupied.
Turning now to the movements of General Smut's army in the south. Colonel Van der Venter, who commanded an important section of the army, crossed the Orange River and occupied a group of stations, including Nabas, Velloor, Ukamas, Jerusalem, and Heirachabis.
On the last day of March, 1915, Van der Venter's force was engaged in several skirmishes in which one man was killed and two wounded, while six of the enemy were killed and twenty-eight taken prisoners. At this price the stations of Platbeen and Geitsaud which yielded a great quantity of supplies and horses and live-stock were occupied.
On April 30, 1915, Van der Venter occupied Warmbad, the railway terminus, without opposition and pushing forward along the line his men entered Kabus, a station sixty-five miles to the north, two days later.
General Smut met Van der Venter at Kalkfontein on April 11, 1915, where plans were laid to drive the Germans from Karas Mountains where they occupied some strong positions. The enemy was attacked in three columns, advancing from different points. Finding themselves threatened on all sides, the Germans made no resistance and abandoned everything.
On April 17, 1915, Van der Venter entered Seeheim, the Germans fleeing in such hot haste that they could not stop to destroy the bridge over the Great Fish River. Colonel Berrange's force which had set out from Kimberley was now in touch with Van der Venter's column. At Hasnur near Rietfontein, Berrange took an intrenched position with slight losses and after frequent skirmishes and hard fighting joined Van der Venter's forces near Keetmanshoop, which surrendered to the combined forces April 20, 1915.
Sir Duncan Mackenzie's column left at Aus now struck out to the northeast with his mounted men and occupied the towns of Bethany and Berseba without meeting resistance and April 24, 1915, reached Aritetis on the railway, seventy miles north of Keetmanshoop, General Mackenzie could now act in conjunction with Van der Venter against the Germans retreating from Seeheim and Keetmanshoop. At Kabus, twenty miles north, in an indecisive engagement with the enemy, the Union forces lost twenty-two men taken prisoners, while the Germans numbering about 600, continued their retreat, their objective being Gibeon, where they hoped to entrain for the capital, Windhoek. General Mackenzie therefore sent a small party to destroy the railway to the north of Gibeon, while the Ninth Brigade was to engage the enemy. This body was defeated by the Germans with severe loss. They took some seventy prisoners and forced the Ninth Brigade to fall back on the main body.