Ugh. Well, guess I'll just stick to earlier editions -- I care too much for consistency to adapt my interpretation all the time, especially when the Chamber Militant fluff is what I "grew up" with and am used to.
As for the Tau, turns out the 4E bit is not a contradiction: The BFG article for Tau Fleets goes into some more detail, explaining it as a consistent development that basically had the Tau use slow "gravitic drives" first, then experiment with a salvaged Warp engine (which they could only use to "dip" into the space between realspace and Immaterium), and finally they combined this engine with the existing gravitic drive to extend the time a ship can spend in this in-between, significantly increasing the range of their ships as they are now effectively "surfing" on the acceleration wave created by the transition.
[edit] added excerpt:
"Once unified by the Ethereal Caste the Tau made incredible technological progress. By M39 they had spread through the T'au system and ringed their homeworld with orbital research and manufacturing facilities. Further expansion required a drive system capable of spanning interstellar distances however and this proved to be a formidable barrier.
Tau vessels already used a form of gravitic drive. This projected a sheath of gravitic energy ahead of and around the vessel which was continually re-projected further ahead, drawing the ship behind it rather like an archaic sail. For two hundred tau'cyr the Water Caste grappled with the problem only for the breakthrough to be handed to them.
On the innermost of T'au seven's moons a routine geological survey discovered the remains of an alien vessel. The significance of the find did not disrupt Tau society as much as might have been expected. Tau theorists had long reasoned that other life forms existed and the verification helped confirm the belief that there was a greater destiny awaiting them. No Tau commented on the sheer good fortune of finding the technology that they so desperately needed on their doorstep just when they needed it.
The Tau were able to duplicate the warp drive of the alien ship but the initial test flights were disastrous. Achieving transition to the Warp required more than technology, it required psychically attuned minds and the Tau race boasted no psykers. Without them to guide the transition no amount of power could breach the dimensional barriers. The best the Tau could do was make a partial transition, forcing themselves into the void that separated Warpspace and real space before they were hurled out again like a ball held under water then released.
Data gathered at great cost during the test flights was studied closely. The Water caste scientists made the observation that the boundary between real space and warp space was not a neat line. It was closer to being a turbulent ocean fomented by the tempestuous warp tides below. By carefully angling their descent toward the Warp and extending the field generated by the gravitic drive into a wing, shaped to hold the vessel down a Tau vessel could extend the duration of the dive considerably. The speeds achieved in the ascent back to real space were staggering and this coupled with the effect of the Warp on time and space ensured that the real distance covered by the dive was immense. Early tests lost several drone ships because they inadvertently passed far beyond the sensor range of their recovery vessels.
The details were soon resolved. There was still a major constraint, only the most powerful (and bulky) drives could sustain the gravitic wing throughout the dive and the power drain meant that considerable recharge time was needed between dives. Also by comparison to actually navigating the warp the pace was still very slow. Taking typical Imperial Warp speeds the Tau drive was slower by a factor of five. The speed was consistent though, did not expose the Tau to the perils of the Warp and enabled the Tau to expand beyond their home star for the first time.
The first major class of Starships built were the ponderous Gal'leath (trans. Explorer). These leviathans laid the foundations for the Tau Empire and formed the basis of the Kor’vattra for its first wars with the Orks and the Niccassar. The Niccassar were less advanced than the Tau and after their speedy defeat were one of the first other races absorbed into the Empire. The Orks however posed a major problem. Their ships were faster, better shielded and more heavily armed. Against such a dangerous enemy the Gal'leath class was simply too expensive a resource to risk. Fortunately new, more compact gravitic drives led to the introduction of the smaller Il'fannor (trans. Merchant) class.
To counter the numerous Ork escorts the Tau developed their own Kass'l (trans. Orca) gunships. The Tau were slow to build a gravitc drive with sufficient power for Warp dives small enough to create an independent escort so the Kass'l would travel inside a larger vessels gravitic sheath over long distances, disengaging when back in normal space. This combined with the introduction of super-heavy ion cannons and barracuda fighters helped restore the balance, but it was the power and efficiency of the Tau shipyards that prevented the Empire from being devastated."
Edited
by Lynata
