The first major assault by Nana Sahib's side took place on the evening of 12 June. However, the attacking soldiers were still convinced that the British had laid out gunpowder-filled trenches, and did not enter the area. On 13 June, the British lost their hospital building to a fire, which destroyed most of their medical supplies and caused the deaths of a number of wounded and sick artillerymen who burned alive in the inferno. The loss of the hospital was a major blow to the defenders. Nana Sahib's forces gathered for an attack, but were repulsed by the canister shots from artillery under the command of Lieutenant George Ashe. By 21 June, the British had lost around a third of their numbers.