We need Airsupport!!!

 The 'Warthog'

The mad Techmarine Hephaeston designed and constructed the first Warthog during the 3rd war for Armageddon. The towering spires of Helsreach were too cramped and dangerous for the Thunderhawks and the chapter itself was unable to rely on the imperial navy for air support. Hephaeston had an idea! A heavily armoured multi role gunship. He designed a ship nimble enough
to take on enemy fighters yet heavily armed and armoured. With it's VTOL capabilities, the Warthog is able to loiter and wreak havoc amongst the enemy.

A well kept secret amongst the Legion is the strange way it carries marines into combat. Underneath the fuselage lies a strange glowing Orb. This device opens up a temporary portal allowing Marines and even Dreadnoughts to pass through, entering the battlefield in a flash of green light. The origin of this device is unknown. Some say is simply the genius of Hephaeston, others.... say it's is salvaged
Xenos technology. To this day is remains a closely guarded secret. Anyone outside the Legion who witnesses its function is quickly whisked away by the Admech for lenghty interrogation. So far, the Legion has avoided coming to blows over this design....so far.

On a realistic note, I wasn't willing to compromise the design to accomade the space needed for 12 Marines and a Dreadnought. Also, this is very much a work in progress.