Joseph Dempsey: AIP Rising - Asia’s submarine evolution
Date: 02 June 2015
By
Joseph Dempsey, Research Analyst, Defence and Military Analysis Programme
As Asian states recapitalise their diesel-electric submarine (SSK) fleets, many are also adopting air-independent propulsion (AIP). This gives submarines greater submerged endurance, bringing associated operational benefits. The typical 5–10-day submerged endurance of a diesel-electric boat can with some AIP systems be extended into weeks, potentially up to a month.
A decade ago, the only AIP boat in the Asia-Pacific was a converted Japanese training submarine; by 2015 more than half the world’s AIP-fitted diesel-electric submarines could be found in the region: China has 12, Japan six, South Korea four, Singapore two and Pakistan one. Though these vessels represent only 17% of Asia’s 150-strong SSK fleet, there is clear evidence of an upward trend, and the number of AIP-fitted SSKs is expected to almost double over the next five years.
Conventional SSKs rely on a limited electrical battery supply for submerged propulsion, risking detection by surfacing or snorkelling in order to recharge with air-breathing diesel engines. AIP provides an auxiliary internal power source for submerged propulsion and/or recharging batteries. Different AIP solutions exist but most prominent are electricity-generating Stirling cycle engines and fuel cells. AIP options exist in a growing number of current and proposed diesel-electric submarine types; the option to retrofit AIP modules into some older designs is also offered.
Submarines are increasingly recognised within Asia as force multipliers, able to counter superior naval forces. As existing operators seek to improve submarine capabilities, others – including Bangladesh, Myanmar, the Philippines and Thailand – are reportedly considering establishing their own submarine services. The wider development and proliferation of submarine-launched land-attack and anti-ship cruise missiles also provide new capabilities, coupled with existing submarine-based intelligence-gathering and Special Forces insertion opportunities.
Though AIP is a costly option, the fact that it can extend the submerged endurance of a submarine represents a key capability enhancement, extending power projection and providing the ability to deliver a sustained sea-denial presence.
AIP also closes the endurance gap between diesel-electric and nuclear propulsion, which can be less attractive in financial, technological, industrial and, often, political terms. Nuclear-powered boats are limited only by crew endurance and provisioning, and can typically operate unsupported for months. Modern SSKs, particularly those fitted with AIP, can also have an acoustic advantage over their nuclear counterparts and their smaller size makes them potentially more suited for operations in littoral waters.
The five early adopters (China, Japan, South Korea, Singapore and Pakistan) continue to expand their AIP fleets – with several key programmes due for completion by 2020 – though the extent of Chinese
Yuan-class procurement is less clear. Other regional navies are also expected to adopt AIP in the longer term. India, for example, intends to equip the last two of its six license-built French
Scorpene-class boats with an indigenous AIP system, and a tender exists for a further six AIP-fitted SSKs. Meanwhile, the competing French, German and Japanese designs for Australia’s
Collins-class SSK replacement are also expected to offer AIP-fitted options.
since this article Pakistan has 3 AIP fitted boats.