The sinking by submarine attack of the Iranian frigate Dena in the Indian Ocean on March 4 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 (EEZ) 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 PNS Hangor’s sinking of the Indian frigate INS Khukri in 1971, the British submarine HMS Conqueror’s sinking the Argentine cruiser ARA General Belgrano in 1982, and a North Korean submarine’s sinking of the South Korean corvette ROKS 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 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.
If a US submarine torpedoes an Iranian warship in the Indian Ocean, it’s sending a message that sea routes on which both China and Australia depend are contestable.
Two-thirds of the planet is ocean, and the law of armed conflict at sea permits hostilities in neutral EEZs so long as sovereign resource rights are respected.
That is precisely the situation off Sri Lanka. The implication for Australia is that any major maritime conflict centred in the Middle East or East Asia will spill across the Indo‑Pacific sea lanes that underpin Australia’s prosperity. Strategic geography cannot be reduced to the tidy boundaries implied by policy documents.
This dynamic also sharpens the China dimension. Beijing already views Middle Eastern conflicts through the lens of energy security and maritime vulnerability. If a US submarine torpedoes an Iranian warship in the Indian Ocean, it’s sending a message that sea routes on which both China and Australia depend are contestable.
The Dena episode also underscores the return of attrition to maritime warfare. The US has destroyed dozens of Iranian warships since it and Israel began attacking Iran on February 28. Levels of combat wastage that would have seemed normal in 1942 are re-emerging in the twenty‑first century.
Australia can learn three things from this.
First, fleet depth matters. A boutique navy composed of a small number of exquisite ships and submarines cannot absorb sustained losses in a high‑intensity maritime conflict.
Each technological wave has transformed but not eliminated the role of surface combatants as the visible, politically purposeful expression of sea power.
Second, industrial and repair capacity becomes decisive. Re-arming, repairing and re-crewing ships may prove as strategically important as the initial order of battle.
Third, training systems must assume losses. Ships, aircraft and crews must be replaceable while sustaining operational tempo.
The presence of Royal Australian Navy personnel aboard the submarine involved in the attack is a reminder that Australia’s alliances will draw it into the realities of sea combat faster than policy debates might suggest.
A tempting but mistaken lesson would be that submarines have rendered surface fleets obsolete. History suggests the opposite. Each technological wave – from the torpedo to naval aviation to precision missiles – has transformed but not eliminated the role of surface combatants as the visible, politically purposeful expression of sea power.
For Australia, this means a credible Indo-Pacific sea-control posture still requires a balanced force: surface combatants, submarines and maritime air power working together.
It also means anti‑submarine warfare proficiency must be strengthened. High‑end anti-submarine warfare is a perishable skill demanding relentless training, realistic exercises and close integration with allies.
Article reprinted with permission from the Australian Strategic Policy Institute's analysis and commentary site The Strategist.