Sivashankar joined the militant Liberation Tigers of Tamil Eelam (LTTE) in 1981 along with T. Sivanesan (Soosai). He took on the nom de guerre "Pottu". Seniority in the LTTE resulted in his nom de guerre "Pottu" being suffixed by "Amman" (uncle). After being trained he served briefly as LTTE leader V. Prabhakaran's bodyguard. He was then sent to Tamil Nadu, India to be in charge of the shore operations in the Vedaranyam area. In 1985, whilst he was in charge of the LTTE's camp in Vedaranyam, he was abducted by rival militant group People's Liberation Organisation of Tamil Eelam (PLOTE). Talks mediated by a former TULF MP failed to result in Pottu Amman's release and so the LTTE's Shankar abducted PLOTE member Jotheeswaran (alias Kannan) who was later exchanged for Pottu Amman.