Lord Chelmsford, the Commander-in-Chief of British forces during the war, initially planned a five-pronged invasion of Zululand consisting of over 16,500 troops in five columns and designed to encircle the Zulu army and force it to fight as he was concerned that the Zulus would avoid battle, slip around the invaders and over the Tugela, and strike at Natal. Lord Chelmsford settled on three invading columns, with the main centre column - now consisting of some 7,800 men - comprising the previously called No. 3 Column, commanded by the Colonel of the 24th Richard Glynn, and Durnford's No. 2 Column,[32] under his direct command. He moved his troops from Pietermaritzburg to a forward camp at Helpmekaar, past Greytown. On 9 January 1879 they moved to Rorke's Drift, and early on 11 January commenced crossing the Buffalo River into Zululand.[5]
The backbone of the British force under Lord Chelmsford consisted of twelve regular infantry companies: six each of the 1st and 2nd Battalions, 24th Regiment of Foot (2nd Warwickshire Regiment), which were hardened and reliable troops.[33] In addition, there were approximately 2,500 local African auxiliaries of the Natal Native Contingent, many of whom were exiled or refugee Zulu. They were led by European officers, but were considered generally of poor quality by the British as they were prohibited from using their traditional fighting technique and inadequately trained in the European method as well as being indifferently armed. Also, there were some irregular colonial cavalry units, and a detachment of artillery consisting of six field guns and several Congreve rockets.[34] Adding on wagon drivers, camp followers and servants, there were around 4,700 men in the No. 3 Column, not including Durnford's No. 2 Column.[35][36] Because of the urgency required to accomplish their scheme, Bartle Frere and Chelmsford began the invasion during the rainy season. This had the consequence of slowing the British advance to a crawl.[37]
Around 10:30 am, Colonel Anthony Durnford, whose left arm was paralyzed from the Xhosa War, arrived from Rorke's Drift with 500 men of the Natal Native Contingent and a Rocket Battery of the No. 2 Column to reinforce the camp at Isandlwana. This brought the issue of command to the fore because Durnford was senior and by tradition should have assumed command.[53] However, he did not over-rule Pulleine's dispositions and after lunch he quickly decided to take to the initiative and move forward to engage a Zulu force which Pulleine and Durnford judged to be moving against Chelmsford's rear. Durnford asked for a company of the 24th, but Pulleine was reluctant to agree since his orders had been specifically to defend the camp.[52]
Chelmsford had underestimated the disciplined, well-led, well-motivated and confident Zulus. The failure to secure an effective defensive position, the poor intelligence on the location of the main Zulu army, Chelmsford's decision to split his force in half, and the Zulus' tactical exploitation of the terrain and the weaknesses in the British formation, all combined to prove catastrophic for the troops at Isandlwana. In contrast, the Zulus responded to the unexpected discovery of their camp with an immediate and spontaneous advance. Even though the indunas lost control over the advance, the warriors' training allowed the Zulu troops to form their standard attack formation on the run, with their battle line deployed in reverse of its intended order.