Direct proof of use
Iraqi T-55-series tanks were documented in the 1990 Gulf War during the February 1991 ground campaign. The U.S. Army Center of Military History records that the 1st Infantry Division destroyed two T-55 tanks in the first hour of VII Corps' attack on 24 February, while Marine forces faced Iraqi T-55 and T-62 tanks in Kuwait and captured the Iraqi 9th Tank Battalion with thirty-five T-55 tanks on the same day.
Additional direct evidence appears in the U.S. Army account of 26 February fighting near Mutla Ridge, where enemy tanks were described as almost all T-55s. Imperial War Museums' collection history for a 16th/5th The Queen's Royal Lancers Gulf War object also describes Objective Lead as a fight against T55s and MTLBs during the British 1st Armoured Division's advance.
Sources: U.S. Army War in the Persian Gulf, IWM 16th/5th Lancers Gulf War Hat
Timeline
The clearest dated T-55 references fall inside the coalition ground offensive from 24 to 26 February 1991. On 24 February, U.S. Army and Marine accounts place Iraqi T-55s in front-line defensive positions and in an Iraqi tank battalion captured by the 2d Marine Division.
On 26 February, the U.S. Army history records T-55-type tanks around Mutla Ridge during the Tiger Brigade's advance. The IWM Objective Lead account describes the British reconnaissance regiment fighting T55s and MTLBs during the same phase of the British advance through Iraqi positions.
Sources: U.S. Army War in the Persian Gulf, IWM 16th/5th Lancers Gulf War Hat
Narrative
The T-55 appeared as part of Iraq's armored and mechanized force rather than as a newly supplied wartime system. During the first day of the ground offensive, Iraqi T-55s were encountered in prepared defensive areas, destroyed in early VII Corps contact, and captured with a tank battalion in the Marine sector.
By 26 February, T-55s were still present in the battles around Kuwait's northern road network and in the Iraqi formations facing British and U.S. armored units. The documented uses point to conventional armored defense, counter-movement, and anti-armor fighting; the sources do not support a complete count of all Iraqi T-55s in theater.
Sources: U.S. Army War in the Persian Gulf, IWM 16th/5th Lancers Gulf War Hat