Operation Prosperity Guardian (OPG), the United States Navy-led coalition of the willing intended to allow international shipping to continue navigating safely through the Red Sea, is set to activate within days. Including allies from Europe and the Middle East, as well as Canada and Australia, the operation has been snubbed by three important NATO countries, France, Italy and Spain.

What is the exact task of OPG?

The official line, “to secure safe passage for the commercial ships”, is too vague for any naval flag officer to feel comfortable getting into. Admirals want politicians to give them precise tasks and clear mandates needed to achieve the desired results.

US ‘plans missile strikes’ on Iran-backed Houthis after Red Sea drone & rocket attacks as Brit warship joins guard fleet

Defining the threat seems easy, for now: antiship missiles and drones of various types carrying explosive warheads have been targeting merchant ships on the way to and from the Suez Canal. All were fired from Yemen, by the Houthi group also known as Ansar Allah which now controls most of the country, including the longest section of its 450km-long Red Sea coast. All missiles were surface-launched, with warheads that can damage but hardly sink big cargo ships.

The Houthis at first announced that they would target Israeli-owned ships, then expanded that to include all those using Israeli ports, ultimately to those trading with Israel. After several attacks where the Israeli connection appeared very distant or vague, it is prudent to assume that any ship could be targeted.

All missiles neutralised by US and French warships so far were shot down by sophisticated shipborne surface-to-air missiles (SAM), proving that the modern vertical-launch systems guided by the latest generation phased array radars work as designed. Many nations earmarked to participate in OPG have ships with similar capabilities. Almost all also carry modern surface-to-surface missiles that can attack targets at sea or land.

If the task of OPG were to be defined narrowly, only to prevent hits on merchant ships, it could be performed using the centuries-old principle of sailing in convoys with the protection of warships.

In a convoy, slow, defenceless commercial cargos sail in several columns at precisely defined distances from each other — led, flanked and tailed by fast warships that can take on any threat. The system is effective, as the United Kingdom, Russia, Malta, and many other countries saved by convoys in World War II can attest.

But every strategy has its limitations. A convoy is big and cumbersome, extending for miles to give behemoth ships a safe distance from each other and to enable them to manoeuvre if needed. Whatever the protective measures taken, huge tankers and container carriers – longer than 300 metres (984 feet) – still present big targets. Captains of commercial ships are generally not trained in convoy operations, and most have no experience operating in large groups or under military command.

Their escorts, even if well-armed, carry a limited number of missiles and must plan their use carefully, allowing for further attacks down the shipping lane and ultimately leaving a war reserve for the defence of the ship itself. Once they expend some of the missiles, they need to replenish them – a task that is possible at sea but done much more quickly and safely in a friendly port out of reach of Houthi missiles.

To clear the critical 250 nautical miles (463km) along the Yemeni coast leading to or from the Bab al-Mandeb strait, advancing at assumed 15 knots (28kmph) — as convoys always sail at the speed of the slowest units — ships would be exposed to even the shortest-ranged Houthi missiles and drones for at least 16 hours.

And before even trying to make the dash, they would be particularly vulnerable in the staging areas in the Red Sea and the Gulf of Aden where ships would spend some time gathering, forming the convoy and setting under way.

The Houthi missile threat is now known to be high, and their arsenal is substantial. Naval planners must be worried by their ability to mount concentrated prolonged attacks simultaneously from several directions.