On 7th February 1987, 'A' and 'C' Companies of the Battalion successfully attacked a terrorist base at Uththamapuram in Kilinochchi. On 10th February 1987 Sinha troops joined the operation launched to re-capture Parantan. As a result of intensified military action the whole Battalion became stationed in the Northern Theatre; the 'B' and 'D' Companies in Pooneryn and the 'C' Company in Mankulam.
Breaching the Cease-Fire Agreement between the Government and the LTTE, the separatists carried out attacks targeting civilians; first on 17th April 1987 at Kithuluthuwa followed by on 21st April 1987 at the Central Bus Stand in Pettah, Colombo. These attacks caused a large number of civilians to be killed and injured many more. Subsequent to these attacks on the civilians by the LTTE the 1st, 2nd and 3rd Divisions of the Army launched 'Operation Liberation '.
The Indo–Lanka Peace Accord of 1987 signed by the Indian Prime Minister and the President of Sri Lanka allowed an Indian Peace Keeping Force (IPKF) to arrive on the Jaffna Peninsula to curb LTTE activities in the North. As part of the ceremonies related to the signing of the Peace Accord, the Prime Minister of India, Mr. Rajiv Gandhi was accorded a Guard of Honour by the Sri Lanka Navy. While inspecting the guard, a naval rating attempted to strike the Indian Premier with the butt of his rifle. Fortunately the Premier warded off the rifle using his arm. The signing of the Accord was not favoured by all sections of society and unruly mobs once again engaged in acts of violence that destroyed property and caused loss of life. It was established that a clandestine 'movement' called the Desapremi Janatha Viyaparaya (Patriotic Peoples Movement - DJV) was responsible for the violence.
On 7th August 1987 the 'D' Company deployed at Parantanwas instructed to report to the newly raised 6thBattalion of the Sri Lanka Sinha Regiment on Battalion transfer basis. Personnel selected from other Companies were made in to a Company and transferred to the new Battalion. Meanwhile, the 'A' Company reported back to the Battalion from Parantan.
The Anniversary Celebrations of the Battalion was held with participation of the Commander of the Army as the Chief Guest on 1st October 1987. After the celebrations the troops from the Battalion were deployed at Isurupaya, Battaramulla for security duties. In the meanwhile 'C', 'D' and 'E' Companies reported back to the Battalion from Pooneryn, Elephant-Pass and Mankulam.
From 25th to 31st December 1987, troops from the Regiment underwent Battalion training at Maduruoya.
In 1988, on 31st January, at the end of Battalion Training at Maduruoya, the Battalion Headquarters and all companies reported back to Ambepussa. However, by 5th February 1988 the Battalion Headquarters and the 'B' Company was moved to Broodie House while the 'E' Company moved in to the Army Sports Control Board building. On 7th February 1988 the 'C' 'D' Companies took over internal security duties at the Deraniyagala and Gampaha Detachments. It was these two Companies stationed at Deraniyagala and Gampaha that jointly presented a Guard of Honour to HE the President, Ranasinghe Premadasa on 11th February at theMahapola exhibition held at Mirigama. The Deputy Minister of Defence and the Commander of the Army too attended this function.
On 26th May 1988 the father of the Battalion, the first Commanding Officer of the Battalion, Brigadier RD Jayatilleka MBE passed away. The cremation took place at the General Cemetery in Colombo with full military honours. As a matter of respect, a large number of both serving and retired military personnel attended.
On 9th August 1988 the Botale Water Project initiated to provide fresh water to the Ambepussa Camp was ceremonially opened by the Commander of the Army, Major General N Seneviratne.
On 16th September 1988 Lieutenant Colonel J Nammuni relinquished duties as the Commanding Officer and same was taken over by Lieutenant Colonel WAA de Silva.
For the first time in the history of the Sri Lanka Army Divisions and Brigades were officially formed and as shown earlier, the Infantry Battalions were placed under command to such Divisions and Brigades.
On 13th March 1989 Lieutenant Colonel GSC Fonseka RWP RSP psc appointed as the Commanding Officer of the Battalion.
Accepting the request made by HE the President, Ranasinghe Premadasa to withdraw the Indian Peace Keeping Force (IPKF) from the Island by 30th March 1990, the Government of India withdrew its troops. The withdrawal of the IPKF followed by the Government holding 'Peace Talks' with the LTTE but failed to strike a deal. On 10th June 1990 the LTTE re-commenced their activities by attacking the Police Stations in the Eastern Province. This marked the beginning of what was termed as 'Eelam War II'.
