context: The film is set in British South Africa, in the province of Natal, in January 1879. The first half of the film revolves around the administrators and officials of Cape Colony, notably the supremely arrogant Lord Chelmsford (Peter O'Toole) and the scheming Sir Henry Bartle Frere (John Mills), who both wish to crush the neighbouring Zulu Empire, which is perceived as a threat to Cape Colony's emerging industrial economy. Bartle Frere issues an impossible ultimatum to the Zulu king, Cetshwayo (Simon Sabela), demanding that he dissolve the Zulu Empire. Cetshwayo refuses, providing Cape Colony with a pretext to invade Zululand. Despite objections from leading members of Cape Colony's high society and from Great Britain itself, Bartle Frere authorises Lord Chelmsford to lead a British invasion force into Zululand.The second half of the film focuses on the British invasion of Zululand and the lead-up to the climatic Battle of Isandlwana. The invading British army, laden with an immense network of supply wagons, invades Zululand and marches in the direction of Ulundi, the Zulu capital. British forces, eager to fight a large battle in which they can unleash their cutting-edge firearm military technology against the vast Zulu army, become increasingly frustrated as the main Zulu army refuses to attack the British, and fighting is restricted to a few small skirmishes between British and Zulu scouts.Concerned that their supply lines are becoming overstretched and that the main Zulu army is still at large, British troops begin torturing captive Zulu warriors in an effort to learn the location and tactics of the Zulu army. Halfway to Ulundi, Chelmsford halts his army at the base of Mount Isandhlwana, ignoring the advice of Boer attendants to entrench the camp and laager the supply wagons, leaving the camp dangerously exposed. During the night, Colonel Durnford (Burt Lancaster) and an escort of 50 mounted Basutos approach the camp. Lord Chelmsford then orders Durnford to return to his unit, bringing them to the camp immediately to reinforce Colonel Pulleine (Denholm Elliott). Lt. Vereker (Simon Ward) should join Durnford as aide-de-camp.Reacting to false intelligence, Chelmsford leads half of the British army, including the best infantry, cavalry and artillery units, on a wild goose chase far from the camp, in pursuit of a phantom Zulu army. On the day of battle (January 22), Durnford and his troops are arriving at 11:00 a.m. at the camp at Isandlwana. Meanwhile, the Zulu captives escape their torturers and regroup with the Zulu army, informing them of the British army's direction and strength. After having lunch with Colonel Pulleine and Lt. Vereker, Durnford quickly decides to send Vereker to scout the hills. Durnford then decides to take his own command out from the camp too, and scout the iNyoni heights.The entire Zulu army is later discovered by men of Lt. Vereker's troop of scouts, who chase a number of Zulu herdsmen, trying to hurry away their cattle, only to discover the main Zulu enemy force of thousands at the bottom of a valley. Lt. Vereker then sends Lt. Raw to warn the camp that it is about to be attacked.As Zulu impis descend upon the camp, Durnford's cavalry retreat to a donga in an effort to hold back the Zulu advance. Forced back, the British take heavy casualties, including the battery of Congreve rockets, which is overrun by the Zulus. Initially, the British infantry succeed in defending the camp, and Zulu forces retreat under a hail of artillery and small arms fire. British units defending the camp are now becoming dangerously spread-out, and are oblivious to Zulu forces moving round the sides of the mountain in an encircling move.As British infantrymen begin to run out of ammunition and the British cavalry are driven back towards the camp, Zulu warriors charge the British troops en masse, sustaining horrific casualties, but succeed in breaking the British lines. As British troops break and flee towards the camp, the battle breaks down into hand-to-hand fighting between British soldiers and Zulu warriors, amongst the débris of tents, fallen soldiers and supply wagons. Overwhelmed by the sheer number of Zulu warriors, British soldiers and their African allies are slaughtered in the camp, some being cut down as they attempt to flee back towards Natal. Colour-Sergeant-Major Williams (Bob Hoskins) sees many of his redcoated men being cut down by Zulu spears. Williams is stabbed in the back by a spear while attempting to save the life of one of his young soldiers, and having killed several Zulu soldiers with his bayonet after he runs out of ammo, dies at the hands of a large band of Zulus.As the British forces break apart, the one-armed Durnford becomes trapped in the camp. Hoping to save his men, Durnford orders his African cavalrymen to retreat. Remaining on foot at the battlefield, Durnford is killed alongside his infantrymen.During the last minutes of the battle, Colonel Pulleine entrusts the Queen's Colours of the 2nd battalion, 24th Regiment of Foot to two junior officers, Lts. Melvill (James Sebastian Faulkner) and Coghill (Christopher Cazenove), who attempt to carry them to safety in Natal, passing gruesome scenes as Zulu warriors hunt down British and African infantrymen attempting to flee across the river. While crossing the Buffalo River, the three lieutenants are cut down by Zulus. Coghill accompanies Melvill in his attempt to gallop the Union Flag back towards Natal. When Melvill nearly drowns while trying to cross the Buffalo River, Coghill turns to help him, and is ambushed by Zulu warriors. Coghill attempts to defend himself with his revolver, but is killed. Melvill is assegaied by Zulu warriors while defending the flag.The Colours (a Union Flag embroidered with the Regiment's insignia) are captured. In his dying moments, Vereker shoots and kills the Zulu wielding the Colours, and the Colours fall gracefully into the river, where they are carried out of reach. Vereker's fate remains unknown (though it is implied that he too gets killed).Seeing the battle lost, Pulleine returns to his tent to pen a last letter to his wife. He is discovered by one of the escaped Zulu prisoners and, unwilling to kill the young soldier, the elderly Pulleine allows himself to be killed in his tent by the Zulu and other warriors that storm in.In the evening, Chelmsford and the rest of the British army return to Isandlwana, to be greeted by the sight of their slaughtered comrades, and the news that a mass Zulu army has invaded Natal and laid siege to Rorke's Drift. Charles L. Norris-Newman (Ronald Lacey), a war correspondent for 'The Standard' also views the devastation (having accompanyed Chelmsford's expecition and so avoid the battle/massacre. The film ends with Zulu warriors in a silhouetted victory procession, dragging captured British artillery back to Ulundi.
question: Who does the British troops blame for the low supply of ammunition?
answer: vast Zulu army