Since mid-November the Houthis have been launching attacks against shipping in the Red Sea. The US sent a number of AEGIS destroyers to help protect international shipping, performing the dual role of intercepting Houthi drone and missiles and coming to the aid of distressed commercial ships.
The British also sent one of its best ships, the HMS Diamond. However something changed leading to the US and the UK to actually strike Houthi military sites in retaliation. What changed?
Serious doubts arose on both the British and US side that it was not equipped to deal with swarms of UAVs and missiles. On January 10, US and British forces shot down 21 drones and missiles. British Defense Secretary Grant Shapps said that doing this was unsustainable. What did he mean?
There are two answers to the question of why the situation with the Houthis was going out of control.
“The [AEGIS] destroyers have a complement of 96 VLS cells, while the [Ticonderoga class] cruisers have 122. …However, they need to fit a mixture of weaponry in those cells so they can’t all be used for air defense. This includes:
ESSM (quad packed into a single cell)
SM-2 (and its newer counterpart the SM-6)
Tomahawk cruise missiles
ASROC anti-submarine missile
SM-3 anti-ballistic missile
The exact ratio of these weapons is largely dependent on the mission and the possible threats faced. However, at least 200 ESSM and another 100 or so SM-2 or SM-6 seems like a fair guess. Maybe a bit more.”
In short, each of the AEGIS has around 100 missiles.
The British Sea Viper air defense system is the main defense system HMS Diamond relied on to fire at Houthi drones and missiles. “Type 45 Destroyers, also known as Daring-class destroyers, are specifically designed around the Sea Viper (PAAMS) air-defence system. Each Type 45 destroyer is equipped with a 48-cell A50 Sylver Vertical Launching System. This system is designed to accommodate a mix of up to 48 Aster 15 and Aster 30 missiles.”
Neither the US nor the British ships can be reprovisioned at sea, so they have a limited ability to “stay in the fight” if it continues for any length of time.
As the January 10 Houthi attack demonstrated, the Houthis were increasing the number of daily attacks. How large an arsenal the Houthis had, therefore, challenged US and British defense capabilities.
One needs to add that using missile defense is very expensive. Each SM-2 missile costs $2.1 million each. Sea viper, which can either be an Aster 15 or Aster 30 costs either £1m to £2m a time ($1.25 million to $2.5 million). Nor does this take into account the challenge of replacing these missiles, once expended. It not only will be more expensive, but could take years of production time.
This leads to the second answer: what happened that was different than before?
There are three possibilities. The first is that on January 10 the British ship HMS Diamond and US destroyers in the area were directly targeted by the Houthis. If this interpretation is correct, it meant that the Houthis decided to directly attack US and UK warships.
The second possibility was Houthi threats and the response by the US.
On December 20, the Houthi leaders warned “they would strike U.S. warships if the Iranian-backed militia was targeted by Washington.” On December 31st the Maersk container ship, the Singapore-flagged Hangzhou, issued a distress call saying it was under attack by four boats. “The small boats, originating from Houthi-controlled areas in Yemen, fired crew-served and small-arms weapons at the Maersk Hangzhou, getting to within 20 meters of the vessel, and attempted to board the vessel,” Central Command said. Helicopters from the carrier USS Eisenhower and the AEGIS destroyer USS Gravely sent helicopters to intercept the four ships. After they ignored warnings, three of the Houthi combat vessels were destroyed by gunfire and the fourth ran away. The Houthis response was “The American enemy bears the consequences of this crime and its military movements in the Red Sea to protect Israeli ships won’t prevent” the Houthis from “performing their religious, moral and humanitarian duty in support and aid of those who have been wronged in Palestine and Gaza.”
But the third reason is more important than shooting up some Houthi boats filled with commandos.
In their attack on January 10 the Houthis fired ballistic anti-ship missiles at US and British warships.
Previously the Houthis relied on Kamikaze drones and anti-ship cruise missiles.
Drones are very slow flying and typically either use small gasoline motors and propellers or are battery powered. The Houthis have four types of combat drones: Qasef-1, Qasef-2K, Sammad-2 and Sammad-3 . The Qasef-1 and Qasef-2 are small loitering munitions based on Iran’s Ababil drone. Each carries a 30 kg warhead. Samad drones are longer range. It is likely the drones used in the shipping lanes near the Bab-el-Mandeb straits are the short range type.
Yemen has a number of different types of anti-ship cruise missiles. On December 11, for example, the Norwegian tanker Strinda was hit by a Houthi anti-ship cruise missile. It sustained some damage but survived. In the Ukraine war a Neptune R360 anti-ship missiles sank Russia’s Black Sea flagship, Moskva. All these missiles are jet powered and subsonic. This means they can be tracked by radar and destroyed with air defense missiles.
The problem is much more difficult if the missiles fired are ballistic missiles, meaning they are powered by a rocket motor. This makes them much faster and gives defenders far less reaction time. The Houthis have many different anti-ship ballistic missiles supplied by Iran. They present a serious problem in restricted sea lanes near the shoreline, which is the key problem facing the allies in the Bab El-Mandeb strait.
It is likely the appearance of rocket powered ballistic anti-ship missiles forced the US and UK to make the decision to finally strike the Houthis and not just stay on the defensive. The only other choice would be to stop protecting shipping in the Red Sea, but that would negatively impact Europe, including the UK, and it would deprive Egypt of its top asset, the Suez Canal, with monthly revenues of around $750 million.