Houthi militias in Yemen launched ballistic missiles at Abu Dhabi and Saudi Arabia on Monday in the latest attack on neighbouring states.
Two missiles were destroyed in mid-flight during the attempted terrorist attack on Abu Dhabi, while in Saudi Arabia, one was shot down and another missile wounded two civilians in an industrial area.
The northern Yemeni militia has, over the past seven years, developed an increasingly sophisticated ballistic missile arsenal, despite a UN arms embargo on the country.
The bulk of the Houthis' arsenal today appears to be made up of the Burkan-3 for longer-range strikes up to 1,200 kilometres, the shorter range Badr P-1 rockets, with a 150km range and the Soviet-era Frog-7, which Houthis call the Zelzal, with a 65km range.
Today, they are known to possess a number of medium-range ballistic missiles — these are weapons defined by the US Centre for Arms Control as having a range of between 1,000km and 3,000km.
Experts and officials have said this can only have happened with external help from Iran and Hezbollah.
What ballistic missiles do the Houthis in Yemen have?
The longest-range ballistic missile in Houthi possession is the Burkan-3.
The Burkan-3 missile is a modified Iranian Qiam missile that can hit targets 1,200km away, the Washington Institute for Near East Policy think tank says.
That estimate is based on analysis by Ralph Savelsberg, a ballistic missile expert at the Netherlands Defence Academy.
It is also inaccurate, especially at the furthest extent of its range, Mr Savelsberg says.
While the Burkan is very similar to the Qiam, the latter is based on a Soviet-era Scud C missile, once feared by US-led coalition forces during the First Gulf War in 1991.
Modern air defence systems such as the US-made Patriot Air Defence and Terminal High Altitude Air Defence systems are highly capable of intercepting such missiles.
These systems have been perfected with more advanced radar and guidance systems over several decades.
The Houthi missiles may sound high-tech, having such a long range, but their ancestry is relatively primitive. The Scud C traces its evolution back to the Nazi V-2 rocket, 1,400 of which hit London in 1944.
The V-2s were terrifying but thankfully the Houthis don't have anything like this number of missiles. Furthermore, the Burkan has a much smaller warhead than the V-2, although the blast would be capable of levelling a house.
In 1947, Joseph Stalin ordered Russian engineers to work with captured Nazi scientists and surviving examples of the V-2 to develop a new Soviet missile.
The V-2 design was reworked into the R1 missile, known by Nato as the SS-1, which was then upgraded with new engines to the R11.
The concept evolved into the Scud missile family, which entered service in the 1970s.
Various countries, including Iran, Iraq (under the Saddam Hussein regime) and North Korea, have all modified Scuds and the Houthi use of the Burkan is only the latest example of this trend.
They, in effect, remain an imprecise projectile that can be fired a long way but with little or no certainty of where they will land.
But attacks have taken a terrible toll within Yemen, where the Houthis have used them at shorter range against civilians.
On October 13, a missile struck a petrol station near the contested city of Marib, killing “dozens”, one of several similar attacks this year. A later attack struck a tribal meeting, killing at least 13 people while another in Marib struck a mosque.
The strikes may seem random but Yemeni government officials say they are aimed at influential local leaders and vital economic infrastructure, breaking international humanitarian law – the Geneva Conventions, for example, prohibits the targeting of civilian infrastructure, or "civilian objects".
How do the Houthis obtain their missiles?
Numerous reports, including a comprehensive UN Panel of Experts investigation in 2020, show strong links between the Houthi missile programme and weapons designed and supplied by Iran.
Tehran has long displayed expertise in building ballistic missiles but in recent years it has improved its accuracy dramatically.
So, too, have the Houthi rebels, who have gone from firing relatively unreliable projectiles blindly towards government-held areas to being able to strike with greater accuracy, as seen in the homing in on specific targets around the government’s last northern stronghold of Marib.
But at greater range, accuracy suffers and warhead size has to be reduced to accommodate more fuel.
The Houthis' missile arsenal
UN weapons inspectors, ballistics experts and the Saudi Arabia-led coalition have analysed evidence, including debris left after strikes and the Yemeni rebels' regular displays of projectiles in propaganda videos, to gain a fair picture of the situation.
During the opening phases of the war in 2014 and 2015 as the rebels seized Sanaa and the international coalition intervened at the request of the government of Yemen, much of the group's weapons systems came from raided military stockpiles and modifications to the plentiful munitions on the battlefield.
However, that has changed over time and experts have increasingly spoken of Iran's hand in helping the Yemeni rebel group to develop and build increasingly sophisticated missiles.
Missiles are modelled on known Iranian weapons and were most likely made in Iran in pieces, smuggled by boat into Yemen then reassembled.
This was confirmed by a US briefing in February 2020 on the seizure of a dhow, which was loaded with missile components bound for Yemen.
"Several components in the interdicted SAMS include the air data computer, the INS, and the vertical gyro, which have all been identified on other Iranian weapons systems," said Centcom, the US general headquarters for the Middle East.