The Capture of Delhi
The siege train, consisting of fifteen 24-pounder guns, twenty 18-pounder guns and twenty-five heavy mortars and howitzers, with almost 600 ammunition carts, arrived on 6 September. Wilson's chief Engineer Officer, Richard Baird Smith, had drawn up a plan to breach the city walls and make an assault. Wilson was unwilling to risk any attack, but was urged by Nicholson to agree to Baird Smith's plan. There were moves among the British officers, in which Nicholson was prominent, to replace Wilson as commander if he failed to agree to make the attack.
As a preliminary step, on 6 September the Company forces constructed "Reid's Battery", or the "Sammy House Battery", of two 24-pounder and four 9-pounder guns, near the southern end of the ridge, to silence the guns on the Mori Bastion. Under cover of Reid's Battery, on 7 September the first siege battery proper was established, 700 yards (640 m) from the Mori Bastion. Four of its guns engaged the artillery on the Kashmir Bastion, while six guns and a heavy mortar silenced the rebels' guns on the Mori Bastion after a long duel. The direction of this attack also deceived the rebels that the storming attempt would be made from the east, rather than the north.
A second battery, consisting of nine 24-pounder guns, two 18-pounder guns and seven 8-inch mortars, was set up near a flamboyantly-designed house known as "Ludlow Castle" in the Civil Lines, and opened fire against the Kashmir Bastion on 11 September. A third battery of six 18-pounder guns was set up near the old Custom House less than 200 yards (180 m) from the city walls, and opened fire against the Water Bastion near the Yamuna next day. A fourth battery of ten heavy mortars was set up in cover near the Khudsia Bagh. Because the element of surprise had been lost, the Indian sappers and pioneers who carried out much of the work of constructing the second and third batteries and moving the guns into position suffered over 300 casualties, but the batteries quickly made breaches in the bastions and walls.
The opening of this phase of the siege seems to have coincided with the exhaustion of the ammunition the rebels had captured from the magazine, as the rebel fire became suddenly much less effective. By this time also, the rebels had become depressed through lack of supplies and money, and by defeatist rumours which were spread by agents and spies organised by William Hodson.
Preparation for the Assault
The attack was scheduled for 3 a.m. on 14 September. The storming columns moved into position during the night of 13 September. The future Field Marshal Lord Roberts, then a junior staff officer, recorded their composition.
- 1st Column â€“ Brigadier General Nicholson
- 2nd Column â€“ Brigadier Jones
- 3rd Column â€“ Colonel Campbell 
- 4th Column â€“ Major Reid
- 5th Column â€“ Brigadier Longfield
Detachments (totalling 200) of the 60th Rifles preceded all the columns, as skirmishers.
There was also a cavalry brigade in reserve, under James Hope Grant, which probably consisted of: