text: Every evening, at an air base in the Saudi capital, Riyadh, coalition spokesman Saudi Brig-Gen Ahmed al-Assiri delivers an upbeat assessment for the media.
  The narrative has changed little since the opening days of "Operation Decisive Storm".
  "We are achieving our aims," says the general. "We are systematically destroying the enemy's bases."
  But what exactly are those aims and are they being achieved?
  When the air strikes began on 25 March the war aims of the Saudis and their allies were simple: reverse the takeover of Yemen by rebels and restore the legitimate president, Abdrabbuh Mansour Hadi, to power. Neither of those two aims has been achieved. Yet.
  Mr Hadi is stuck in a guest palace in Saudi Arabia, effectively in exile, while his remaining support base withers away in Yemen.
  The poorly-armed but determined southerners trying to defend the city of Aden from the Houthi northerners grumble that their president fled the country, leaving them to fend for themselves.
  The Houthis, who began their takeover of Yemen by overrunning the capital Sanaa in September, have certainly taken a battering from the air strikes. But on the ground they have remained largely in control of the whole of western Yemen where the population is concentrated.
  Their success is due, not so much to any alleged support from Iran, but to the help they are getting from renegade former President Ali Abdullah Saleh, who has backed them with Republican Guard and other military units still loyal to him.
  The rebels come from the far north of the country, and as Shia they share the same branch of Islam as only 30 percent of the population; the remainder are Sunnis.
  So they know they probably cannot hold onto the south indefinitely and will announce a strategic withdrawal once they feel they have made their point, namely that they have survived the onslaught of several air forces and their US-made precision guided missiles.
  The Saudis have a lot resting on this campaign.
  The new defence minister, Prince Mohammed bin Salman, is only 34 years old and relatively untested.
  If the campaign fails it will reflect badly on him but more importantly on his father, King Salman.
  So the Saudi leadership knows it cannot afford to fail in Yemen, not just for fear of instability spilling across their common border but also for what it means for their own credibility amongst the Saudi people.
  Periodically there are reports of Saudi armour moving closer to the Yemen border, prompting speculation about a ground offensive.
  But everyone knows Yemen can be a graveyard for invaders.
  Its rugged, mountainous terrain and fiercely territorial tribesmen make it an extremely difficult country to fight in. Ask the Egyptians, the British and even latterly the Saudis, who have all taken casualties there.
  So any ground incursion by the Saudi-led coalition is likely to be a temporary measure - such as, say, throwing a cordon sanitaire around Aden - to secure a better bargaining position when the political negotiations begin in earnest.
  Iran, whose exact role in Yemen is somewhat murky, has called several times for a ceasefire, accusing their regional rivals, the Saudis, of committing genocide there.
  On Monday, their foreign minister suggested it was time to choose a new government, with Iranian help. The Saudi reaction was apoplectic.
  "It's an absolute non-starter," a Saudi adviser told the BBC. "The new Saudi doctrine is to have an Arab world free of any Iranian role. It's typical delusional rhetoric coming out of Tehran."
  So how exactly will this war end? In fact, can it end? Probably messily is the answer.
  Three weeks in there are no clear winners or losers, unless you count al-Qaeda which is profiting from the turmoil in the east of the country.
  Ultimately, there will have to be a political settlement, a compromise deal that is just about acceptable to all parties, otherwise one side or the other will simply carry on fighting.
  "The Saudis always wanted a political settlement," says a retired Western diplomat.
  "I can understand why they wanted to do this [campaign] but they need to define victory and that has not been done. Right now the Houthi [rebels] are the ones controlling the narrative."
  However this ends, Saudi Arabia will be instrumental in Yemen's future. Up until now, it has been one of the country's principal benefactors.
  Along with other Gulf Arab states, Saudi Arabia has no wish to see Yemen collapse and has poured millions of dollars into the country. If the Houthis were to remain in power it is hard to see that financial tap being turned back on.
target: For almost three weeks the Saudi-led coalition of mostly Gulf Arab air forces has been pummelling Houthi rebel positions across Yemen.