There is one ground war plus two air wars currently underway in Yemen.
The ground war engages the Houthi rebels against al Qaeda and ISIS fighters in support of Yemen's Sunni regime.
One air war is being waged by Saudi and other Sunni air forces against the Houthi rebels - and the rest of the Houthi civilian population for that matter. The Saudis love dropping those made-in-USA cluster bombs on Houthi villages. You could very fairly say that the Saudi and Sunni coalition air forces are flying air support missions for al Qaeda and ISIS forces, also Sunni in the radical Saudi fashion.
Then there's that other air campaign. This is the fledgling American bombing campaign against AQAP (al Qaeda in the Arabian Peninsula) forces in Yemen. It is no small irony that everyone on the ground in Yemen on both sides is getting hammered by America-built jets delivering America-built bombs.
The last strike took place on March 28, when US warplanes hit AQAP fighters stationed at “the headquarters of Brigade 27 near the city’s airport, an air defence camp and the house of the commander of the second Military Region” in the city of Mukallah, the provincial capital of Hadramout, Reuters reported. The number of casualties has not been disclosed.
Yes, that's right. al Qaeda is using Yemeni government military installations. In other words, Sunni militants are the Yemeni home team.
Why doesn't the USAF just cut out the middle man and simply shoot down the Saudi, Egyptian, Kuwaiti, Moroccan, Jordanian and Qatari warplanes which would allow the Houthis to get on with the business of pushing al Qaeda and ISIS out of Yemen. Then, once America's F-15s turn the Saudi F-15s into lawn ornaments they can negotiate the sale of the next batch.