Colombo is deftly playing New Delhi against Beijing. 
The Rajapaksa brothers, undisputed--and unchallenged- rulers of Sri Lanka have perfected the game over the past decade by playing on India's insecurities about increasing Chinese presence in its immediate neighbourhood. Of late, the strategy has been taken to a new level with Sri Lanka openly disregarding India's concerns.
Alarm bells started tolling louder in New Delhi this past month when reports about a Chinese nuclear submarine docking in Colombo first surfaced. Although Sri Lanka's Navy Chief, on a visit to India, accepted that a Chinese submarine did visit Colombo he denied it was a nuclear-armed, nuclear-powered submarine. Within days of his admission, another Chinese submarine--Changzheng 2-- made a port call in Colombo on its way for a mission to the Gulf of Aden on November 2. New Delhi regards this development as inimical to India's strategic interests and has reportedly told Colombo that such encouragement to China is unacceptable.
Sri Lanka watchers are however not surprised with Sri Lanka's gambit.
For the past decade, President MahindaRajapaksa and his hawkish brother, Defence Secretary GotabayaRajapaksa have increasingly turned to China for military aid and support in international fora after New Delhi, then ruled by the United Progressive Alliance (UPA) government, dithered over various issues thanks to domestic political compulsions.
For instance, when Sri Lanka launched its military offensive against the Liberation Tigers of Tamil Eelam (LTTE) in 2005, New Delhi was caught in two minds. As a country, India wanted LTTE to be ruthlessly eliminated. The ruling UPA led by the Congress Party was however heavily dependent for survival in Parliament on the DMK, a Tamil Nadu-based party considered a close ally of the LTTE. So an open support to any Sri Lankan military action by the Manmohan Singh government would have created political instability in India.
To be fair though, Colombo did turn to India for help. In late 2005, President Rajapaksa sent his brothers Basil and Gotabaya to New Delhi with a shopping list for essential weapons and equipment that the Sri Lankan armed forces needed to launch a military offensive against the LTTE.
Initially, New Delhi was non-committal. Publicly New Delhi maintained that it would not give Sri Lanka any offensive weapons.
Yet, in early 2006 India quietly gifted five Mi-17 helicopters to the Sri Lankan Air Force. The only Indian condition was: these helicopters would fly under Sri Lankan Air Force colours. New Delhi clearly did not want to annoy UPA's Tamil Nadu allies like the DMK unnecessarily. The Mi-17s were in addition to a Sukanya Class offshore patrol vessel (OPV) gifted by the Indian Coast Guard to the Sri Lankan Navy.
But hampered by domestic compulsion, New Delhi could not go beyond such meagre and clandestine transfer of military hardware. The Rajapaksa regime was nothing if not shrewd. It was also conscious of India's anxiety in losing strategic space in Sri Lanka. So it quickly approached Beijing for material help. China was more than willing. Military hardware, including armoured personnel carriers, ammunition for small arms on favourable credit terms was immediately supplied.
The Sri Lankan forces won a famous military victory in 2009 but the allegations of massive human rights violations during the final phase of the war pushed Colombo on the back foot. Initially, after the end of the war, New Delhi went so far as to support the Sri Lankan government in a special session at the United Nations Human Rights Council (UNHRC) on 28 May 2009, voting against a motion that called for an investigation of war crimes. India also helped Colombo in the post-war reconstruction effort by providing financial assistance for infrastructure projects and humanitarian assistance for the displaced population.
 Post-2009 however, domestic pressure in Tamil Nadu forced the Indian government to join international calls for an investigation of human rights violations and war crimes. In a significant departure from its previous approach, in March 2012 and March 2013, New Delhi voted in favour of U.S.-sponsored UNHRC resolutions that asked the Sri Lankan government to fulfill its commitments and take actions to ensure justice, accountability and reconciliation (2012) and to carry out an independent investigation into alleged human rights law and humanitarian law violations (2013), respectively. 
This was a substantial shift in New Delhi's approach, which had always been opposed to country-specific resolutions and to interference with the internal affairs of third countries. Colombo did not take this change in India's stance kindly. The most obvious example of domestic politics casting a shadow over India's policy towards Sri Lanka came in November 2013 when the 23rd Commonwealth Heads of Government Meeting (CHOGM) was held in Colombo.  The Sri Lankan government had wanted to use this event to regain international legitimacy after the controversy over the UNHRC votes and the repeated doubts on its human rights record. 
The participation of India's Prime Minister in the CHOGM meeting was therefore considered absolutely essential. A broad coalition of actors from Tamil Nadu forced the weakened Manmohan Singh to boycott the meeting despite the foreign policy establishment's argument against it. Officials in the Ministry of External Affairs pointed that New Delhi needed to keep some leverage on the Rajapaksa regime if only to get the Sri Lankan government to work for the welfare of minority Tamils in Sri Lanka. However, after a huge domestic debate, Prime Minister Manmohan Singh ultimately decided not to participate in the CHOGM further alienating Colombo. 
Since then Colombo drifted away from New Delhi. 
Not the one to forget or forgive easily, President Rajapaksa appears to have decided to let Beijing have a free run in Sri Lanka. A couple of months ahead of the Presidential elections (scheduled for early 2015), Mahinda Rajapaksa is perhaps hoping to bolster his 'tough leader' image by taking on 'mighty' India. In doing so however, he may have allowed Sri Lanka to once again become a playground for big power rivalry.r
The writer is Security & Strategic Affairs Editor with Indian Broadcaster NDTV