Question Details: I don’t understand why the attack failed, and why the rebels were able to escape. Part of this involves the mistake that the general made re: pulling out of hyperspace too early. I don’t understand that element, but I think there is more to understand re: what happened.
Let me start by correcting you a bit, with a scene from The Empire Strikes Back between General Veers and Darth Vader:
VEERS
My lord, the fleet has moved out
of light-speed. Com-Scan has
detected an energy field protecting
an area around the sixth planet of
the Hoth system. The field is
strong enough to deflect any
bombardment.
VADER
(angrily)
The Rebels are alerted to our
presence. Admiral Ozzel came out
of light-speed too close to the
system.
VEERS
He felt surprise was wiser…
VADER
He is as clumsy as he is stupid.
General, prepare your troops for a
surface attack.
VEERS
Yes, my lord.
It’s glossed over pretty quickly as you mentioned, but here’s a basic tactical summary, based on my personal experiences in Extraterrestrial Defense and FTL Navigation Principles:
Hyperspace travel consumes and radiates an enormous amount of energy for even a single ship – note the bright “flash” of light whenever a ship drops back to relativistic speeds in the movies. These energy bursts should thus be easy to detect, and probably form the basis of most tactical naval intelligence in the Star Wars universe.
It stands to reason, as well, that placement of the detection equipment could have an enormous effect on the total range of such sensors… And, since the Rebel Alliance is trying to hide their presence completely on Hoth, it also makes sense that they would not use any orbital, or even system-wide detection satellites for the job – since doing so would allow the Empire to surmise a hostile presence of some kind without needing to engage in costly and time-consuming searches by Probots.
So, we’re left with the following: planetary surface dishes/arrays which, like our own Earth-side radio and optical telescopes, have a much shorter effective range compared to space-based equivalents, and which have a much harder time picking smaller, subtler signals from the noise created by the atmosphere, solar radiation, etc.
With all of the above as background, I submit the following:
By exiting hyperspace too close to the planet/system, the Rebels on Hoth were able to detect the incoming fleet of Star Destroyers, giving them time to raise their energy shield, and force the Empire into a more costly ground engagement.
If Admiral Ozzel had, instead, opted to exit from hyperspace further out – say 5-10 AU, it’s likely that the hyperspace signatures of the fleet would’ve escaped detection, which in turn would’ve allowed them to approach slowly, and fire a large, concentrated, and continuous barrage of beam and impact weaponry – or perhaps even going the most sophisticated/stealthy route, and towing large rocks from the nearby asteroid belt, and hitting the rebel base with them(*).
As for the attack itself failing:
It again is a result of poor asphyxiated Ozzel’s gaffe – the Empire went from simply interdicting/capturing/destroying the Rebels at their whim, to needing to make a more obvious frontal assault on their shield generators.
This in turn allowed the Rebels to enact counter-strategies in advance based on the most likely scenario – AT-AT walkers supported by speeders and ground troops. This may also explain why the snowspeeders are all equipped with magnetic grapple guns – if you think about it for a moment, there doesn’t seem to be too many other potential military uses for such, and if it was a wholly-improvised solution imagined by Luke Skywalker, it is unlikely that the filament cabling would’ve been “randomly up to the task” of tripping up a blaster-proof metal beast with 30′ legs.
These delaying tactics, plus a concerted defense of the shield generators, would possibly allow for the comparatively calm/orderly retreat depicted in the movie.
(* Even a near-miss by a 1km-wide boulder travelling at, say, .0001c (or, as I call it, “mach 90“) at impact, would cause such apocalyptic damage that any survivors would likely expire within minutes if not hours – and the dust and ash thrown skyward would drastically hamper the operation of any air or spacecraft which subsequently attempted to leave the surface – think a couple thousand Eyjafjallajokull-level volcanic eruptions occurring simultaneously, and you get the idea.)
This answer originally appeared on Quora: What were the battle dynamics re: the Imperial attack on Hoth?
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