Success in Yemen would establish Riyadh as de facto leader of the region's Sunni states
Saudi Arabia's campaign to stop the Houthis from ruling over Yemen could define its role in the Middle East for years and shape its regional struggle with the rebels' ally Iran.
Success would establish Riyadh as de facto leader of the region's Sunni states it has pulled together in a complex armed operation, and embolden it to pursue a more assertive stance against what it sees as the expansionist ambitions of its arch rival Shi'ite Iran in Iraq, Syria, Lebanon and Bahrain.
But failure could hamper Riyadh's ability to persuade allies and neighbours to join it in future ventures and deal a public setback to its new monarch King Salman as well as other senior princes early in his reign.
"This campaign has confirmed that Saudi Arabia is the heavyweight power in the region. But they've taken a risk," said Abdulkhaleq Abdulla, a political scientist from the United Arab Emirates.
"If this thing fails, Iran is going to be much more emboldened and in this region there's usually a zero-sum game between Tehran and Riyadh. This is a test for the new king and Saudi Arabia," said Abdulla.
Riyadh wants to reinstate some stability and its own influence in Yemen by ensuring President Abd-Rabbu Mansour Hadi is strong enough to force his opponents to negotiate.
The kingdom's previous experience in fighting the Houthis, during a brief border war in 2009-10, relied on US satellite imagery, while its participation in air strikes against the Islamic State group in Syria has also relied on American command and control.
This time it is not only striking targets across the country from the air without US help, but it is also overseeing operations by allied aircraft, coordinating the role of several naval forces and preparing ground troops.
While Riyadh has not ruled out a ground operation, analysts close to Saudi thinking believe an invasion across the frontier, which would play to Houthi strengths, is very unlikely, although it is possible it will deploy special forces inside the country.
Riyadh's tough military campaign is matched by an ambitious political plan: to use the air strikes and sustained pressure from a coalition of Arab states and Pakistan to drive the Houthis to the bargaining table and force them to deal.
Saudi Arabia's enormous firepower during the last war with the Houthis was described by the U.S. Riyadh embassy in a cable leaked to WikiLeaks as "imprecise" and "minimally effective".
A senior US official told Reuters on Thursday the latest operation was a "panic response" by Riyadh to the fast-deteriorating situation in Yemen and that the coalition had been assembled so quickly its effectiveness was in doubt.
Despite Wednesday night's strikes, Houthi fighters advanced towards Aden on Thursday and were fighting in the city's outskirts as the president departed the city for the Arab League summit via Riyadh.
If the Houthis manage to take Aden in the coming days despite the Saudi-led strikes, and to stop Hadi returning to the country, a crucial war aim of Riyadh's 10-country coalition will have been rapidly defeated.
Any setback of that nature would provide a keen test of the coalition's political strength, already somewhat fragile. Pakistan contradicted early Saudi statements that it was part of the coalition on Friday, saying it had not yet decided whether to join.
Saudi Arabia's proud claim to be a moral leader of the Muslim world will also be tested should it sustain casualties among its own fighters or accidentally kill Yemeni civilians through misdirected strikes.
For King Salman, who only assumed power in January after the death of his predecessor Abdullah, failure could dent his personal authority and prestige outside the country.
The same is true for his son Prince Mohammed, who as Defence Minister has become the face of the campaign, appearing alongside his cousin, Interior Minister and Deputy Crown Prince Mohammed bin Nayef, directing operations on television news.
On Al-Arabiya channel, which is closely associated with the Salman branch of the ruling Al Saud family, the footage of the pair visiting an air base as the strikes began was accompanied by stirring martial music.
One observer warned that Saudi Arabia might be focusing too much on military strategy and not enough on the political strategy and negotiations that could follow should its military plan work.
"There's got to be a political end point. The goal...was that there should be a legitimate government that could be sustained. I'm not sure that looks obtainable given the Houthi advance," said John Jenkins, head of theInternational Institute for Strategic Studies in Bahrain and a former British ambassador in Riyadh.