After some searching around on the net have found the quote relating to them. It's listed as
WD#161 (although looking at the cover of that issue, with a Chaos Dwarf Lamasu, I don't think that issue contained this so the reference might not be correct).
But, I do vaguely remember this from the old 1st edition Space Marine rulebook (perhaps a William Hill, or Bill Hill as he was back then, story?)
Mighty ships began the descent from orbit, hoping to overwhelm the defenders by sheer weight of numbers. Unlike the drop-pods these presented fine targets for weapons of the defenders. And thus did the battle lasers blasted many renegade ships from the sky, sending thousands of tons of fused metal death down onto the ground below. One giant craft span out of control and crashed into a hab-unit, killing a hundred thousand people. Another was welded to the ground, disgorging its passengers into a lake of bubbling tar and plas-crete. The vessel of the Warped Dogs was vaporised and that Titan Legion's name passed into history.
Interestingly I found another modern extract. (This must be from the board game rulebook, rather than Collected Visions, I've looked through the latter and any mention of the destruction of whole Titan legions is omitted).
The quote is exactly the same, except Warped Dogs is replaced by Legio Damnatus, continuing the modern
GW tradition of replacing it's cool, characterful 80's names that had initially been invented down the pub, with pretentious pseudo-latin.
Anyway, just for the sake of it here are some cool pieces of classic titan art
