The Thunderhawk’s big older brother and predecessor, the Stormbird was to the Legiones Astartes of the Great Crusade what the Thunderhawk is to the Astartes Chapters of the 41st Millenium: a primary means of transport and air support for Space Marines. The Stormbird, however, was much bigger, able to carry up to 50 Space Marines as well as dreadnoughts and rhinos, protected by void shields, and armed with a ton of firepower. So it was basically an Imperial Manta for all intents and purposes. It replaced the Skylance used by the Thunder Warriors.
By the time of the Horus Heresy, though, while some of the bigger Legions insisted on keeping their Stormbirds in service, most had begun relying more and more on the smaller and easier to produce Thunderhawk. After the Codex Astartes reforms, the ability to carry half a company’s worth of marines all in one aircraft wasn’t even arguably economical anymore, and the remaining Imperial Stormbirds were finally mothballed. A rare case of a weapon disappearing from the Imperium's arsenal, not so much because of a lost ability to produce it, but because it simply didn't fit into the changing playbook of Astartes tactics anymore. One would think they would have re-purposed them for anti-Titan operations, into heavy bombers or for transporting vehicles full time. However in the Imperium efficiency and creative thinking is considered Tech Heresy.
As of the 41st Millennium, it’s currently unknown if there are any Stormbirds still left in Loyalist vaults, though Traitor Legions like the Word Bearers are said to still have a few around, and if Forge World’s recent release of the model and 40k rules for the Stormbird is anything to go by, odds are there probably will be a couple of chapters that will be revealed to, surprise, surprise, still have their Stormbirds as well.
It is interesting to note, though, that Forge World's stormbird is almost an entirely different aircraft from the one pictured in older fluff. Where the old Stormbird looked like a giant Valkyrie with two tiltrotor turbofan engines each almost as big as the aircraft itself, the Sokar-pattern Stormbird is basically just a Thunderhawk on steroids (The old Stormbird was also fluffed as having a 100-marine carrying capacity, rather than the Sokar's 50). A bit odd, as Forge World has generally tried to maintain the Rogue Trader look when updating the old material.
As it turns out, the Sokar is simply one of several very different patterns of the same general classification of aircraft (unlike the Thunderhawk, the Stormbird is not a standard template design), and the Sokar itself is actually among the smallest of them. Legions variously fielded Condor (Sons of Horus), Khonsou, and Apophis (the Wolves deployed 30 on Prospero) pattern stormbirds, the latter being known as "sun-killers" for their size and appearance. There was also the Warhawk-pattern Stormbird, which can carry 100 marines like the Rogue Trader version and, given its description as "monstrous and fat-bodied", likely looked like that version as well.
One notable Stormbird is the one Nathaniel Garro had pimped out for his personal use by Malcador so that he could cruise around the galaxy hunting down members for his loyalist A-Team.
Funnily enough, the reasons the Imperial Manta was mothballed in the fluff are also kind of represented in the crunch. The Stormbird is one of those units that could be tentatively referred to as Mega-Super-Heavies (like the Reaver, Warlord, and the actual Manta for instance). Units that are just so big and so expensive that outside of the very biggest games (as in, boards where Basilisks run out of range), they have close to zero practicality. In the case of the Stormbird, a Thunderhawk probably would be a more economical option most of the time. With all that said, though, the Stormbird certainly delivers your points worth. The Stormbird has 14/13/12/ and 12 HP. It comes with five turreted Twin-linked Lascannons (so right then and there, you got more laser dakka than a Terminus Ultra), six Dreadstrike Missiles (S10 AP2 Ordnance, small blast) which can be replaced with a single use 3D6 Apocalyptic Barrage that hits like a Battle cannon. It can buy an Orbital Strike, with Strength D AP1, Massive blast, Indirect fire only and multiple use for the low, low price of 150 pts. Its 2 Void Shields can become a 12" bubble if you go into hover mode, which is a safe idea since you also get Armoured ceramite and a 5++ invul. Transport capacity of 50 can carry pretty much everything including Dreadnoughts and (possibly fully loaded) Rhinos which take up 10/25 slots respectively. Good thing the Age of Darkness FoC limits you to 25% spending on LOWs and no one actually has the money to play Apoc with FW, right?
The only image of a Stormbird people had for years (and the basis for many an awesome scratch-build) before Forge World came out with the Sokar Pattern.
One of said scratch-builds. The new Stormbird model is cool and all, but work like this kinda makes you wish Forge World had stayed closer to the original. This one also seems to have a case of divided loyalties, given that it is painted in Ultramarine colours and has omegas, but also has both Iron Warriors and Imperial Fists symbols.
|Forces of the Adeptus Custodes|
|Command:||Companions/Hetaeron - Shield-Captain|
|Troops:|| Allarus Custodians - Aquilon Terminator - Custodian Guard |
Custodian Warden - Sagittarum Guard - Sentinel Guard
Vexilus Praetor - Warder
|Walkers:|| Contemptor-Galatus Dreadnought - Telemon Heavy Dreadnought |
Venerable Contemptor Dreadnought
|Transports:||Coronus Grav Carrier - Drop Pod - Grav-Rhino - Rhino|
|Vehicles:|| Caladius Grav-Tank - Dawneagle Jetbike - Gyrfalcon Pattern Jetbike |
Pallas Grav-Attack - Venerable Land Raider
|Flyers:||Orion Gunship - Stormbird|
|Titans:||Warlord-Sinister Pattern Battle Psi-Titan|
|Auxiliaries:||Sisters of Silence|
|Forces of the Death Guard|
|Leaders:|| Chaos Lord - Daemon Prince - Sorcerer - Chaos Champion |
Malignant Plaguecaster - Plague Surgeon - Tallymen
|Troops:|| Biologus Putrifier - Blightlord Terminator - Chaos Spawn - Deathshroud |
Foul Blightspawn - Noxious Blightbringer - Plague Marines - Possessed
|Vehicles:||Chaos Land Raider - Helbrute - Plaguereaper - Predator - Rhino|
|Flyers:||Storm Eagle - Stormbird - Thunderhawk|
| Blight Drone - Defiler - Foetid Bloat-Drone |
Myphitic Blight-Hauler - Plague Hulk - Plagueburst Crawler
|Daemons:||Nurgling - Plaguebearer|
|Auxiliaries:||Cultists - Pestigors - Plague Zombie - Poxwalkers|
|Allies:||Chaos Daemons - Chaos Space Marines|