The whole exchange is really worth reading, however, and so, with Collin’s permission, I’ve published it below. Enjoy!
The Diplomat: What is Indonesia’s submarine doctrine?
Koh Swee Lean Collin: As we all understand, Indonesia is a vast archipelagic country, which correspondingly means that effectively and comprehensively policing its vast maritime expanses poses a unique challenge. This thus also shapes the way the Indonesian Navy (or TNI-AL) prioritizes and builds its force structure in view also of the persistent resource constraints.
Submarines certainly form a major facet of the whole game plan. Their role is intended largely in peacetime to constitute a “fleet-in-being” deterrent to any potential foe. In wartime, due to the multiplicity of possible sea approaches the adversary may undertake, it is necessary to carry out effective sea denial using submarines, by focusing them on the strategic SLOCs [Sea Lines of Communication] of the highest priority.
To effectively accomplish this feat, Indonesia's ideal submarine fleet strength has to hover around eight at the minimum, and 12 ideally. Historical experiences had a role to play in deciding the envisaged submarine capacity TNI-AL should have. During its “golden age” in the 1960s, the TNI-AL had up to 12 Soviet-built submarines of the Whiskey class.
However, for the foreseeable future, TNI-AL seemed to realize that 12 boats could be financially implausible to attain, hence eight would be the best [number] to strive for. However, as we see today, the TNI-AL remains a distance from this intended target. With the new trio of South Korean-built submarines ordered recently, at the very most there'll be just five boats including the existing pair of Type-209s. It is most likely that not all boats will be operational at any one time.
Hence, the peacetime role of “fleet-in-being” deterrent and wartime sea denial role will remain the centerpiece of TNI-AL submarine doctrine. A limited sea control role would be possible in specific contexts, but more effective sea control over the Indonesian archipelago [only] appears more possible with a further expansion of TNI-AL's submarine force. More likely, the three South Korean-built boats will be the only operational boats gradually supplanting the aging pair of 209s, by then too old and less cost-effective to operate and maintain.
Why was the Palu Bay selected to serve as Indonesia’s submarine base?
The primary reasons for selecting Palu surely have to do with geography. It's located, first of all. astride the Strait of Makassar and the Palu Bay is a narrow, deep inlet (reportedly 400m) which provides maximum security for the submarine force in terms of concealment and defense against attacks. Besides its sitting astride the strategic waterway, Palu offers direct access northwards into the Sulawesi Sea, where Indonesia still has an outstanding dispute with Malaysia over the Ambalat offshore oil block, off the Malaysian-controlled Ligitan and Sipadan Islands (which were awarded to Kuala Lumpur in the early 2000s by the International Court of Justice). The historic loss of the islands to Malaysia made it even more imperative for Indonesia to safeguard its rights over the Ambalat block. This was also taken into account during previous naval standoffs between the two countries' maritime forces in 2005 and 2009.
Therefore, the significance of Palu Bay is to facilitate TNI-AL's ability to project a submarine presence into the Ambalat, and perhaps to serve as a form of deterrent against unilateral naval moves by the Malaysians whose existing Scorpene class submarines were based nearby in Sabah's Sepanggar. In fact, in 2009 Indonesia suspected that Malaysia had deployed the submarines in the disputed waters, leading to the RMN chief to assure Indonesian legislators that KL would not make such moves. Whether or not it had assured Jakarta of this remains debatable, but the Palu Bay would offer TNI-AL a form of insurance against potential Malaysian naval moves into the waters. It is not inconceivable that TNI-AL subs would be well poised to conduct covert surveillance in the Ambalat waters, keeping track of unusual Malaysian activities in the area.
From a broader perspective, the Palu base is also part of the TNI-AL's overall reorganization efforts, fronted by the expansion from two existing fleets — the Eastern and Western Fleet Commands — to three, including the new Central Fleet Command. This appears to be a move to reorganize the division of labor of the TNI-AL more equitably into distinct geographical areas of responsibilities. It also signifies the increasing strategic importance of the central waterways of the Indonesian Archipelago, which are believed to be the arena of foreign submarine activities. TNI-AL's Palu base hence should also be seen in this light. However, the Palu base also has another focus down south, as I explain in greater detail in the following question about the strategic waterways.
To what extent, then, is Indonesia trying to gain the capabilities necessary to exert more control over the shipping routes it is located upon, potentially being able to interdict shipping from specific countries during a conflict?
I believe Indonesia is certainly seeking to exert greater control over the three main strategic waterways - Lombok, Makassar and Sunda. These are often relegated to secondary importance after the Malacca Strait, which carries greater economic value. However, the geostrategic location of Indonesia means that its archipelagic waters would become the conduit for foreign naval movements to and fro the Indian and Pacific Oceans. This certainly includes foreign submarine activities, as mentioned earlier.
The Indonesians have long been conscious of the vulnerability of these waterways to foreign naval activities, which Jakarta deemed as rather disconcerting, especially with the rise of major power rivalries and tensions in the region, which correspondingly amplifies the importance of these waterways. For many years since 2004, the TNI-AL has focused a significant portion of the maritime surveillance assets to counter piracy and sea robberies in the Malacca Strait and to deter separatism in the Papuan province, as well as to the Ambalat waters. It's therefore time for the Indonesians to place more attention on the three strategic waterways.
However, the tasks at hand for TNI-AL are daunting, given the emergent need to refocus attention on the Natuna Islands, where the South China Sea tensions and recent PLA Navy forays deep south in the area (as exemplified by the PLA Navy's “show of might” near James Shoal at the southernmost rim of the South China Sea) have created renewed concerns. To accomplish all these tasks, including greater control over the strategic waterways, Indonesia would have to expand its current naval forces in multiple dimensions, including surface, subsurface and land-based maritime aerial support elements.
We have recently seen procurement and force restructuring efforts that appear to be geared towards this mega effort. More emphasis has been placed on enhancing surface and aerial surveillance capabilities, while the earlier mention expansion from two to three fleet commands are all manifestations of this endeavor. This will certainly continue to be an incremental, gradual enhancement process which takes time, and until then the TNI-AL could only best hope for intermittent control over the waterways instead of round-the-clock ability to do so. One only needs to note the extremely daunting task TNI-AL faces in acquiring, operating and maintaining a capacity sufficient to police the entire archipelago.
Submarines hence serve as a useful force in the effort to exert greater control over those strategic waterways, which are geographically ideal for subsurface actions in times of peace and war. The proximity of Palu base to these three waterways (Makassar astride, and Sunda and Lombok down south across the Java Sea) facilitates TNI-AL's submarine presence in those areas in both periods of peace and contingencies. However, in view of the small size of the TNI-AL submarine fleet even with the entry of the new boats, the best it can hope for presently remains primarily sea denial and at best, limited amount of sea control in those three waterways. The Palu base certainly serves as a “force multiplier” in this respect.