From Wikipedia "Anglo-Zulu War:
Weapons
Shaka is credited with introducing a new variant of the traditional weapon, discarding the long, spindly throwing weapon and instituting a heavy, shorter stabbing spear. He is also said to have introduced a larger, heavier cowhide shield, and trained his forces to thus close with the enemy in more effective hand-to-hand combat. The throwing spear was not discarded, but standardised like the stabbing implement and carried as a missile weapon, typically discharged at the foe, before close contact. These weapons changes integrated with and facilitated an aggressive mobility and tactical organisation. Although Shaka's introductions achieved comparative success in the earlier stages of the war, they were to be technically outclassed later on by more modern British firearms such as the Martini-Henry rifles.
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Use of modern arms
The Zulu had greater numbers than their opponents, but greater numbers massed together simply presented yet more lucrative, easy shooting in the age of modern firearms and artillery. African tribes that fought in smaller guerrilla detachments typically held out against European invaders for a much longer time, as witnessed by the 7-year resistance of the Lobi against the French in West Africa, or the operations of the Berbers in Algeria against the French.[citation needed]
When the Zulu did acquire firearms, most notably captured stocks after the great victory at Isandhlwana, they lacked training and used them ineffectively, consistently firing high to give the bullets "strength." Adaption to firearms was well within Zulu capabilities and knowledge. Southern Africa, including the areas near Natal was teeming with bands like the Griquas who had learned to use guns. Indeed one such group not only mastered the way of the gun, but became proficient horsemen as well, skills that helped build the Basotho tribe, in what is now the nation of Lesotho. In addition, numerous European renegades or adventurers (both Boer and non-Boer) skilled in firearms were known to the Zulu. Some had even led detachments for the Zulu kings on military missions.
The Zulu thus had clear scope and opportunity to master and adapt the new weaponry. They also had already experienced defeat against the Boers, by concentrated firearms. They had had at least four decades to adjust their tactics to this new threat. A well-drilled corps of gunmen or grenadiers, or a battery of artillery operated by European mercenaries for example, might have provided much needed covering fire as the regiments manoeuvred into position.
No such adjustments were on hand when they faced the redcoats. Immensely proud of their system, and failing to learn from their earlier defeats, they persisted in "human wave" attacks against well defended European positions where massed firepower decimated their ranks. The ministrations of Zulu witchdoctors, or the bravery of individual regiments were ultimately of little use against the volleys of modern rifles, Gatling guns and artillery at the Ineyzane River, Rorke's Drift, Kambula, Gingingdlovu and finally Ulindi.
A tough challenge
Undoubtedly, Cetshwayo and his war leaders faced a tough and extremely daunting task - overcoming the challenge of concentrated rifled, machine gun (Gatling gun), and artillery fire on the battlefield. It was one that also taxed European military leaders, as the carnage of the American Civil War and the later Boer War attests. Nevertheless, Shaka's successors could argue that within the context of their experience and knowledge, they had done the best they could, following his classical template, which had advanced the Zulu from a small, obscure tribe to a respectable regional power.