From Elite manual
Cobra MK I
Combat-trader craft favoured latterly ny pirates, the Mark I Cobra was the first trade ship designed and build for the one-man trader. Its special feature at the time fo manufacture (by Paynou, Prossett and Salem) was its Prossett Drive, which incorporated afterburners with proton-tightened, interior shaft walls. These are now a standard fitting for both internal and external integuments of all PPS made crafts
Cobra MK III
Larger, more popular version of the Cobra Mk I (the Mk 2 only reached prototype stage and was abandoned due to a design fault in the hull). This shio is equipped with severak soecuak features, including Zieman Energy Deflection Shields, fore and aft, and mountings for four Ingram Pulse lasers. The Cobra is much favoured by lone-wolf traders who wish to combine potential superior combat qualities wuth adequate cargo space.
The Cobra Mk III is a classic all-purpose ship found throughout human space. The model was first built in Lave Cowell & MgRath shipyard in Lave in 3100. Despite its age, it remains a popular ship for lone pilots who value its balance of carrying capacity and ability in combat.
Source: The Game's website.
The Cobra MkIII is a larger and more popular version of the Cobra MkI. It was first seen in service in 3100 AD, originally manufactured by Cowell & McGrath Shipyard, Lave. Since Cowell & McGrath's acquisition by Faulcon DeLacy it is now branded as a Faulcon DeLacy made ship.
The Cobra's carrying capacity, being more than double that of the Hauler, and its cost, being almost one third that of the Type-6, makes it a logical stepping stone for aspiring traders as there is no other ship capable of hauling more cargo at the Cobra's size and cost. In addition to its large cargo hold it has much better combat potential than freighters and can defend itself or run away from hostile interdictions. What's more is that the Cobra is an ideal craft to plunder the space lines in for a pirate or smuggler due to the Cobra's ample capacity for loot, the ability to outrun most other ships and its relatively low heat signature.
The downside of this ship is the combat ability relative to other ships. For bounty hunters who are attempting to tackle skilled opponents the Cobra MkIII can be outmanoeuvred by Eagle MkIIs and Viper MkIIIs while being easily outgunned by Pythons and Anacondas.
The Cobra MkIII is also a good and affordable exploration ship due to the sizeable Fuel Tank (x16) and the amount of Internal Compartments which allows for the placement of the necessary exploration modules such as a Discovery Scanner, a Detailed Surface Scanner, a Fuel Scoop and a Auto Field-Maintenance Unit without the need to remove the shield.
Source: The Alpha Orbital "Elite Dangerous" information site.
The Cobra Mk IV is Faulcon deLacy's development of the famous Cobra Mk III. It's a heavier and bulkier ship than the Mk III, but packs an extra punch and better weaponry placement makes it a more effective combat vessel. It's tougher to improve survivability and allows better upgrading, but at the expense of some of its agility.
Source: The Game's website.