For all the bluster of Saudi generals who vow to lead their troops into Sana'a if necessary, the campaign now has more limited goals, says the confidant. Saudi Arabia wants to send Iran and its regional clients a message that it will resist their regional push. With Iran holding sway through its proxies in Baghdad, Damascus and Beirut, Saudi Arabia is loth to let a fourth capital, particularly one in its back yard, go Iran's way. But the campaign is now mostly about blunting the capabilities of the Houthis (a militia of Zaydis, a splinter Shiite sect concentrated in Yemen's north) and their ally, Ali Abdullah Saleh, who until Saudi Arabia engineered his removal in 2012 was the Arab world's longest-reigning ruler.

Together the Houthis and Mr Saleh make a formidable force. Whereas the former are guerrillas who model themselves on Lebanon's Hizbullah, the latter commands Yemen's Republican army, which has been fighting wars (including against the Houthis) for 25 years. Together they wield an arsenal of tanks, ballistic missiles and, at one point, even the odd fighter-jet. Houthi fighters head to battle carrying charms, such as keys and visas to paradise. Their preachers on satellite television call for re-establishing Zaydi rule across the border, not just over the three border provinces the Al Sauds seized in 1934 but even over Mecca farther north.

That is implausible given Saudi Arabia's air power and network of allies. But some Saudis ask how their overfed armed forces would fare should battle-hardened Houthi fighters make even a limited push across the border. It says much about Saudi trepidation that General Olyan limits himself to defending Saudi territory; he says his troops make no attempt to attack the Houthi heartland of Saada governorate, just across the frontier.