The Dreadclaw Assault Pod (or just the Dreadclaw) is the older, more advanced pattern of Drop Pod used during the Great Crusade, and possibly even earlier. They have many major advantages over their current Imperial counterparts, but chief among them was that they could take off and fly on their own, even after landing- in essence, they functioned as assault boats as well as drop pods and could even be used for boarding action against enemy voidships. Some even suspected their Machine Spirit was dangerously close to true Abominable Intelligence. The big problem was...well how to put it? These pod's Spirits were not very nice. Space Marines who went in sometimes ran into 'accidents'. Rather nasty ones. Safety harnesses suddenly unbuckling mid-descent. Crew pods jettisoned in space. Failure of backthrusters to turn on. Passengers mulched by whirring machinery...while most people kind of accepted these rare and small costs, some worried and began to look deeper. If it wasn't obvious then, something was indeed fucking obvious when Horus declared his rebellion. Suddenly, the rate and amount of accidents was drastically increasing on loyalist pods, while rebel pods would do the kitty cat equivalent of purring contentedly on the traitors' laps. These kind of machinery-accidents spread on Imperial vessels during the Horus Heresy, to the point where many Imperial Navy admirals just jettisoned their Dreadclaws into the void of space when their Machine Spirits started sabotaging launch bays and maintenance decks on the starships where they were kept. After the Heresy, while no one could really figure out what was wrong, it was deduced that there was a deep, Chaotic flaw in their design, so the Imperial fleets who hadn't already done so had their remaining stock destroyed.
The Chaos Space Marines of course kept theirs, and so to this day have a huge advantage in space operations. I suppose if you needed proof that there was something wrong with the Dreadclaws, for one, daemons aren't all that willing or even able to possess the damned things, and they still happily continue their service mostly mutation free. Oh and they don't seem to mulch Chaos crews like they did with their old Imperial ones.
The Dreadclaw first received rules in Imperial Armour Update 2006, after the Space Marines got provisional Drop Pod rules in Imperial Armour Update 2002 and Chapter Approved and then proper rules in their 4th edition Codex. Forge World also made a model for them at this time.
Forge World also used to make Dreadclaws in Battlefleet Gothic scale to depict Chaos Space Marines' boarding torpedoes, but that ended in 2013 along with the rest of Forge World's and Games Workshop's Specialist Games figures.