Slitherine

Are they able to attack units? They have an attack against infantry icon but I can't get them to do an attack even against infantry.
Thanks.

No. They have no action points (AP). The attack stats are there so they can at least defend themselves.

Thanks. What is their best use?

They are only useful in the only Marines DLC mission they appear as aux. units IMO.

And I completely forgot that you can buy them for your core. My advice: don't.
Take a recon plane instead.