The Strait of Malacca is the world's busiest shipping lane, with more than 94,000 vessels passing through each year. Yet during periods of geopolitical tension in the Indo-Pacific, major navies often avoid sending nuclear submarines and aircraft carriers through it. Instead, they take the longer route via Indonesia's Lombok Strait and Makassar Strait.
The reason is not distance or convenience. It is water depth.
The Strait of Malacca has a minimum depth of only 25 meters. In narrow sections such as the Phillip Channel, the depth falls to just 19–23 meters. By comparison, the Lombok Strait is 200–250 meters deep, while most of the Makassar Strait exceeds 250 meters, reaching 680 meters at the Dewakang Sill.
That difference determines whether a nuclear submarine can remain fully submerged and undetected, or must surface and lose its greatest tactical advantage.
Because the Lombok Strait has become a preferred submarine transit route, it has also become a prime location for underwater surveillance.
Evidence emerged in April 2026, when a local fisherman discovered an unmanned underwater vehicle (UUV) marked "CSIC," referring to the China Shipbuilding Industry Corporation, floating north of Gili Trawangan along the Lombok Strait.
Such vehicles are commonly used to monitor and track submarine movements, suggesting that underwater intelligence operations in the strait are already taking place—not just existing as theoretical scenarios.
Why Depth Matters
Nuclear submarines require a deep water column to operate stealthily, ideally at depths of several hundred meters. In the Strait of Malacca, where the minimum depth is only 25 meters, submarines have little room to remain fully concealed beneath the surface.
As a result, submarines crossing Malacca are often forced to travel near or at the surface, sacrificing the stealth that defines their strategic value.
Conditions are very different in the Lombok Strait. There, submarines can maintain normal operating depths of 150–300 meters throughout their transit, making them far more difficult to detect.
The Sunda Strait, another western route through Indonesia, offers little advantage. Its minimum depth is only about 20 meters, making it even shallower than the Strait of Malacca.
Why Aircraft Carriers Also Avoid Malacca
Aircraft carriers face a different challenge from submarines. Their draft, the portion of the hull below the waterline, is only about 11 to 12 meters on Nimitz and Ford-class carriers. This is well below the Strait of Malacca's minimum depth, meaning they can technically pass through the strait without running aground.
The real concern is strategy. The Strait of Malacca is narrow and heavily congested, leaving carrier strike groups with limited room to maneuver. During a crisis, they are also easier to monitor and more vulnerable to attack.
The Lombok and Makassar Straits provide a better alternative. Both are wider, deeper, and less crowded, giving large naval formations greater operational flexibility.
These routes are equally important for commercial shipping. Very Large Crude Carriers (VLCCs) with capacities of 200,000 to 320,000 deadweight tons, as well as bulk carriers above 230,000 tons, cannot pass through the Strait of Malacca because their draft exceeds its depth. They must instead sail through Lombok or Makassar.
Protected by International Law
The strategic importance of the Lombok and Makassar Straits is not based on geography alone. Their role is also recognized under the 1982 United Nations Convention on the Law of the Sea (UNCLOS).
As an archipelagic state, Indonesia is required to designate Indonesian Archipelagic Sea Lanes (ALKI) for international navigation.
There are three official routes. ALKI I passes through the South China Sea, Karimata Strait, and Sunda Strait. ALKI II runs through the Lombok Strait, Makassar Strait, and Flores Sea. ALKI III consists of several routes across eastern Indonesia.
Under UNCLOS, foreign vessels, including warships, have the right to continuous and expeditious transit through these sea lanes. However, they are prohibited from conducting military exercises or using weapons while passing through.
Among the three routes, ALKI II is both legally recognized and physically the most suitable route for submarines and large vessels.
Lombok Has Been a Strategic Route for Decades
The Lombok Strait has played a military role for decades. During World War II, Allied submarines, including the U.S. Gato-class and Dutch O-class, used its deep waters to attack Japanese convoys.
Throughout the Cold War, submarines from both the United States and the Soviet Union used the same route to monitor Pacific naval movements and gain access to the Indian Ocean.
The discovery of a CSIC unmanned underwater vehicle near the Lombok Strait in April 2026 suggests that this strategic competition is still ongoing.
Its importance is expected to grow further under the AUKUS defense partnership. Australia's Collins-class submarines already conduct regular transit exercises through the strait. Beginning in the 2030s, the future SSN-AUKUS nuclear-powered submarines are expected to make 8 to 12 transits each month from Darwin.
The Strait of Malacca may remain the world's busiest shipping lane, but when global navies need a route that offers both depth and stealth, they choose Indonesia's waters instead.
