My first thoughts were about the old Frigates in 41 millenia universe. The few chapters which still have a few of them, guarded like chapter relics.
IMO SM chapters would have updated their weapon systems during these 10000 years.
So, Space Marines don't use Stormbirds nowadays, they use T-hawks instead, and bombardment cannons.
I agree Horizon about the torps, the model doesn't have it. Therefore, Frigates would be the only pure gunships of the actual SM navies:
4 hits (2 shields) or 6 hits (one shield), 25-30 cm (+1d6 to AAF), turn 90 , armor 5+, 2 turrets.
Main weaponry, always for port & stardoard sides:
Heavy lance version: 45 cm. str. 2 (L/F & R/F, fire arcs like Eldar Void Stalker)
Possibly of 3 str. 30 cm. Bombardment cannon (L/F & R/F, fire arcs like Eldar Void Stalker)
Launch Version: 1 launch bay for each side, thunderhawks
Weapon batteries: 6 str. 30cm.
