As the U.S. Navy Just Demonstrated, War at Sea Is Global

The sinking by submarine attack of the Iranian frigate Dena in the Indian Ocean on 4 March is a blunt reminder that maritime war does not respect the tidy geographic boundaries favoured in policy frameworks. It also exposes a deeper problem for Australia: a navy built around a handful of exquisite ships and submarines is not structured for sustained attrition in a conflict that will not remain neatly contained.

Legally, the strike also sits squarely within contemporary law‑of‑naval‑warfare doctrine. Enemy warships are lawful military objectives by their nature, location and use. Their targetability does not depend on proximity to a declared theatre of operations, nor on whether they are engaged in immediate combat. Dena’s presence in international waters inside Sri Lanka’s exclusive economic zone didn’t diminish its status as a lawful target. Even the reported issuance of warnings, unnecessary when attacking warships, did not alter the fundamentally orthodox character of the engagement.

Submarine-on-warship kills are rare but not abnormal. Dena is only the fourth such case since 1945, following the Pakistani submarine Hangor’s sinking the Indian frigate Khukri in 1971, the British submarine Conqueror’s sinking the Argentine cruiser General Belgrano in 1982, and a North Korean submarine’s sinking of the South Korean corvette Cheonan in 2010. Each case involved a single torpedo salvo destroying a combatant. The Dena strike was not an innovation in naval warfare but the modern reappearance of a traditional undersea doctrine, amplified by far deadlier technology.

For Canberra, the most uncomfortable aspect of the sinking is not legality but geography. The frigate was reportedly destroyed about 20 nautical miles (about 36 km) off Sri Lanka, well outside the Gulf, yet directly astride trunk routes critical to Australia’s economic security. The Indian Ocean, the Arabian Sea and the approaches to the Malacca and Lombok Straits are not peripheral to some distant theatre of war; they are the theatre.