Operation Liberation (commonly known as the Vadamarachchi Operation) was launched after months of planning on 26 May 1987. Colonel Wimalaratne was one of the field commanders of the operation, serving as the Brigade Commander of the 1st Brigade which consisted of the 1st Gemunu Watch and 1st Gajaba Battalion. The brigade group consisting of the 1st Brigade and 3rd Brigade, commanded by Brigadier Denzil Kobbekaduwa it was the largest formation deployed by the Sri Lankan Army at that point and the first conventional battle to take place in the civil war. The objective was to take the territory of Vadamarachchi in the Jaffna peninsula from LTTE (Tamil Tiger) control. 1st Brigade broke-out of Thondamanaru area with the infantry wading across the lagoon, but was stopped by a mine-field. With the combat engineers clearing a path across, 1st Gajaba Battalion broke-out and reaching the coast, troops from the 1st Brigade defeating the defensive line commanded by the LTTE leader Soosai, made a 90 degree turn undertaking a pincer movement capturing Valvettithurai. By 31 May, the government declared that the Vadamarachchi region recaptured. During the operation Kobbekaduwa and Wimalaratne were nearly killed when the house closed to them exploded due to a bobby-trap.
