The standard air support and transportation vehicle for the Space Marines. Comes in two variants, the Thunderhawk Gunship and the Thunderhawk Transport. The gunship variant can hold thirty Space Marines inside (or fifteen Terminators, three Dreadnoughts, or some combination thereof), and sports the massive Thunderhawk Cannon (or a Turbo-Laser) on its back. The transport variant has two clamps on the recessed underside, for carrying either two Rhinos or one Land Raider underneath it. Both variants have missile/bomb pylons and multiple remotely-operated twin-linked heavy bolter turrets on the wings and hull.
The Thunderhawk replaces the Stormbird transporter, which is larger, more heavily armed and capable of carrying more cargo than a Thunderhawk Gunship and Transporter combined, up to 50 Space Marines. As the demand for dropships increased during the Great Crusade, the Thunderhawk was created as an easy-to-produce alternative for the Unification War era Stormbirds, though considered inferior in quality. After the Horus Heresy, it was decided that putting one twentieth of a Space Marine Chapter in a single vessel was a bad idea, so the Stormbird was mothballed after the Codex Astartes reform.
The Thunderhawk started out life in Epic as essentially a flying Rhino (in other words, they were METAL BOXES); it had a stumpy battle cannon and wings three scale feet thick. This persisted through a number of horrendous-looking scratchbuilds before eventually someone at Games Workshop had the bright idea of producing a limited-edition £400 Thunderhawk in lead for 40K, with a much longer hull, proper, manly wings, and loads of weapons. These were given away as the non-useless prize for winning Golden Demon along with the usual Slayer Sword a couple of times, until GW saw there was a Market and Forge World took up the slack. Forge World still sells Thunderhawk models, both in Transport and Gunship varieties, with several options for molded livery and (for the Transporter) vehicles to be carried.
Also known as the Aetos Dios because people can't type Æ. The Ætos Dios is a modified Thunderhawk exclusive to the Imperial Fists Primarch, Rogal Dorn. It would be befitting that Rogal would have his own personal jet plane fit for a Primarch. The Ætos Dios differ from the regular Thunderhawk with its Turbo-Laser and its single Titan Void Shield. Making it a flying Titan. (AKA the Flying Rape Machine)
In terms of tabletop the Ætos Dios is usable in games of 3000+ points as a dedicated transport and have the IWND special rule and a 4+ invulnerable save against all missile attacks. It also doesn't take up a Lord of War slot.
Interestingly enough, the flying rape-engine was first conceived
after following several failed attempts on Rogal Dorn's life following the outbreak of the Horus Heresy. Mago Telluria constructed for Dorn a unique, heavily-customised personal Thunderhawk gunship to both convey him in battle and to shield him as he conducted missions in the defence of Terra.