Houthi drone boat attack shows growing use of tactic

Small craft laden with explosives are difficult to spot and intercept

A drone boat captured from Yemen's Houthi rebels. AP

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Houthi militias in Yemen hit a commercial ship in the Red Sea with an explosive drone boat on Wednesday, the first successful attack of its kind since the group began its blockade of the waterway in November.

The ship, a bulk carrier called Tutor, is apparently out of control and taking on water, having been catastrophically damaged, according to the UK Maritime Trade Organisation.

Unmanned drone boats are small motor boats that travel on the surface, or slightly below, remotely piloted and driven into ships to detonate their cargo of explosives.

This has several advantages over typical Houthi drone or ballistic missile attacks on ships, which cause damage or start fires on top of the ship's hull, but do not necessarily sink it if the waterline is unaffected. The Houthis also possess anti-ship cruise missiles optimised to sink warships, but they are more expensive than the drone boats.

The Houthis said on Wednesday they had carried out a “military operation targeting the Tutor ship in the Red Sea, using a naval drone, aerial drones and ballistic missiles”.

The Houthis have used the boats on numerous occasions during the conflict, but so far not successfully. The group pioneered the combat use of the unmanned weapon when they struck a Saudi vessel in 2017.

In the Second World War, Imperial Japan also used a similar tactic, launching Shinyo, or “sea quake”, boats at US ships, although these were manned, since radio control of vessels was in its infancy. Insurgents and terror groups including Al Qaeda, Sri Lanka’s Tamil Tigers and Hamas have also used the weapon, but also in its manned form.

So common is the tactic against commercial ships in the Red Sea – transit point for about 12 per cent of global trade – that the UKMTO – a government body – has issued instructions to crews expecting their use. UKMTO uses military jargon, calling them Water Borne Improvised Explosive Devices.

“WBIED attacks may result in a breach of the ship’s hull. The use of the safe muster point is recommended before entering a citadel located below the waterline. If a WBIED is anticipated, the time to react is very short,” UKMTO said.

How can boat-bombs be stopped?

The US and UK, and a number of other countries, have so far successfully intercepted the drones, as well as bombing their launching sites in waves of air strikes.

But once launched, the vessels are particularly dangerous. Attacking by day, they can at first appear in the distance as crewed motor boats, UKMTO warns. This is a significant threat to commercial ships, which lack military-grade optical devices, such as the Mark 20 Electro-Optical Sensor System available on US warships, which allows crews to identify small boats at long range, day or night.

They are also a serious threat to naval forces, as evidenced by their extensive use in the Black Sea in the Ukraine war.

Ukraine has invested heavily in the weapons, which have sunk numerous Russian warships.

Countermeasures are still in development – especially for when the drone boats attack at night – and in some cases, Russia has resorted to using netting around ports.

In choppy waters, drone boats that are low in the waterline are even harder to spot, both visually and with radar, which struggles to create a clear picture as beams encounter the “clutter” of moving seas.

Other innovations being worked on by Ukraine include drone boats capable of firing rockets, missiles and even carrying anti-aircraft systems.