Indonesia's recent US$1.1 billion move to buy three diesel-electric submarines from South Korea highlights the growing complexities beneath the waves of East Asia as the region's undersea build-up continues apace. Regional analysts, naval officials and scholars say the purchase of the updated Type-209 submarines will not shift the balance of power in a region where navies, large and small, are upgrading and/or acquiring submarine fleets. However, it could potentially complicate long-favoured undersea routes, they say. The Indonesian archipelago has several strategically vital deep water trenches and island passages that link the Pacific and Indian Oceans. While the shipping choke point of the Malacca Strait is among the world's most important shipping lanes, the strait is too shallow for submarines to travel submerged and therefore undetected. United States submarines, for instance, have instead discreetly used the Makassar and Lombok straits, while Australian submarines have also been frequent visitors, monitoring Indonesia as well as regional military activity. Increasingly, other navies with expanding blue-water ambitions and long-range submarine capabilities - particularly China, with its nuclear-powered fleet, and Russia, as well as possibly neighbouring Singapore and Malaysia - are expected to regularly transit Indonesian waters, say Asian and Western naval officials. Japan, South Korea, Vietnam and Malaysia are all expanding fleets while the Philippines and Thailand are considering their first purchases, but it remains to be seen how ambitious these navies will be with their deployments. Stealthy submarines are sought after for their ability to protect a vast coastline by deterring far larger navies. They also provide a secret intelligence role, able to tap undersea communications cables as well as spy on electronic signals and military movements far inland. While Indonesian officials have yet to detail how their new submarines will be used, some regional scholars believe Indonesia's interests are strictly coastal, rather than harbouring any wider ambitions. 'There is little doubt the Indonesians will be using these vessels for covert surveillance within their maritime space, monitoring the activities of foreign navies,' said Dr Sam Bateman, an Australian-based senior fellow at Singapore's S. Rajaratnam School of International Studies (RSIS). 'Obviously, that will be a complicating factor for the navies using these straits and passages - activity that is almost certain to increase. 'The Indonesians have long been very sensitive about the activities of foreign navies within their [maritime] domain, and I'm not sure that is always well understood.' Bateman and fellow RSIS scholar Collin Koh Swee Lean have recently warned of the dangers of collisions or misunderstandings stemming from increased submarine activity. 'On the one hand, the confined Southeast Asian maritime geography - characterised by semi-enclosed and narrow water bodies - makes for excellent submarine operations [though a bane for anti-submarine hunters],' Koh wrote recently. 'On the other ... this provides an ideal recipe for potential incidents, inadvertent or otherwise.' He urged greater regional co-operation, particularly in the neglected field of submarine rescue. But veteran US submariners say even with the expected rise in activity, the risk of collisions remains minute, given the sheer scale of the undersea domain, even in key channels. Rescue co-operation, however, is an area that could be used as a confidence-building measure despite the sensitive nature of submarine work. The US has expanded its submarine fleets in the Pacific, including re-building facilities in Guam (the US territory nearest to China), and has expanded deployments, focusing on China's naval build-up as well as North Korea's. Dr Ian Storey, a regional security scholar at the Institute of Southeast Asian Studies, said Indonesia would struggle to use the submarines to their full capacity, given the complexity of submarine work and training. The new submarines will be used to replace two German-built vessels that the Indonesians have used intermittently over the last three decades. Storey's recent book, Southeast Asia and the Rise of China, notes the geo-strategic importance of deep-water channels through Indonesia's archipelago. For instance, he describes US submarines using the Ombai-Wetar Strait north of East Timor. $9.29b Indonesia's projected military spending, in US dollars, by 2015, an increase of 46 per cent over this year's sum, according to IHS Jane