Why was it a mistake to come out of hyperspace close to Hoth?

Question

From the script:

Alarms sound throughout the hidden Rebel base.  In the control room, a 
controller urgently gestures for General Rieekan to check a computer 
scan.

            CONTROLLER
    General, there's a fleet of Star 
    Destroyers coming out of hyperspace 
    in sector four.

            RIEEKAN
    Reroute all power to the energy 
    shield.  We've got to hold them till 
    all transports are away.  Prepare 
    for ground assault.

Rieekan exits hurriedly.


[...]


            VADER
    What is it, General?

            VEERS
    My lord, the fleet has moves 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.

Why exactly was this a bad idea, and what was Vader's preferred strategy? The Rebels can apparently raise their shield instantly, so it seems like they would do that anyway, surprised or no. In fact, since being surprised gives them less time to prepare, it seems like this is a good strategy on the Empire's part.

Is the issue that the Imperial forces didn't have enough time to prepare, and it would have been better to come in farther out and spread out, as this answer says? If so, why wouldn't forming up while already in the system also give the Rebels warning, and give them even more time to escape? All I can really think of is that they would have somehow known the range of the Rebel sensors, dropped out of hyperspace just past them, formed up, then quickly flown into range, but that seems hard to infer from the exchange between Vader and Veers.

Answer 1

This is addressed in some detail in the Star Wars: Battles that Changed the Galaxy factbook. Notably, Ozzel deviated from the Empire's standard battle tactics without speaking to Vader first, largely out of an abundance of caution and the impulse to win a quick victory. In practice he achieved the opposite by underestimating his opponent.

• Vader was anticipating that they would approach Hoth under the cover of its extensive asteroid belt.

An extensive asteroid field snarled in-system travel, and regular asteroid impacts on Hoth created thermal signatures that would hide signs of habitation. If such signs were detected, observers would most likely conclude that yet another band of smugglers was trying to use Hoth as a bolthole.

• Instead Ozzel took it upon himself to jump out of hyperspace right next to the planet, which theoretically would have been safer for his ships and more effective in catching the Rebels by surprise. They were, however, much better armed (and crucially, defended by a planetary shield) than was anticipated.

Standard tactics called for Ozzel to assemble his squadron on the edge of the Hoth system and approach using its asteroid belt as cover, but Ozzel feared the rebels would call in the Alliance fleet, catching his task force amid the chaos of the asteroids. So he opted for surprise, decanting from hyperspace close to the planet. The rebels activated a planetary shield to protect their base—a potent defense the Empire did not know they had. Furious, Vader strangled Ozzel and promoted Firmus Piett in his stead. With an orbital bombardment now impossible, General Maximilian Veers moved immediately to execute a ground assault: he would land Blizzard Force’s dozen AT-ATs beyond the shield’s perimeter, march overland to the shield generator, and destroy it

---

Pablo Hidalgo addressed this failure in strategy in Star Wars Insider #72

Q. Vader said that [Ozzel] emerged from hyperspace too close to Hoth when attacking the Rebel base there. Why was that a problem?

PH: The strategy of the Imperial Death Squadron was supposed to be to emerge from hyperspace at a greater distance from Hoth, organize into attack formation, and then move inward to bombard the planet. Such regrouping is standard since maintaining combat formation over long hyperspace jumps is difficult. Ozzel brought the fleet out within Rebel sensor range, before the Imperials had organized for bombardment, thinking that the surprise would allow the Empire to easily defeat the Rebels. The Rebels were alerted to the Imperial presence and raised their planetary shields. What was to have been an easy orbital bombardment then became a costly and prolonged ground engagement. Vader corrected the strategic flaw by removing Ozzel from command, permanently.

Answer 2

Darth Vader's strategy was to exit hyperspace on the perimeter of the Hoth system and drift into Hoth orbit undetected. From the Wookieepedia article on The Battle of Hoth:

Vader and many of his top officers had planned a sneak attack, jumping out of hyperspace at some distance from the planet and taking advantage of the fact that the meteor activity made it difficult for the Rebels to spot approaching ships. They would then initiate limited long-range orbital bombardment to destroy the base, along with any spacecraft and defenses. Major General Maximilian Veers would then mount a sweeping ground assault to capture any survivors.

Admiral Ozzel foiled this plan by jumping in too close - from the Wookieepedia article on Hyperspace:

An interesting phenomenon associated with hyperspace travel was Cronau radiation. This was a short, but powerful burst of radiation which was generated when a ship entered and left hyperspace. It could be detected by properly aligned sensors from a few light-seconds away, often well outside normal sensor radius. This was how the Rebel base on Hoth was able to prepare for the oncoming attack when Admiral Ozzel mistakenly took the Executor and its battle fleet out of hyperspace too close to the system, rather than approaching stealthily from outside the system.

Conceivably, a single missile disguised as a meteor could have taken out the Rebel base's power or shield generator before the shield could be raised (witness how the Imperial probe droid approached Hoth undetected).

Now whether "Cronau radiation" was canon when The Empire Strikes Back was written, I don't know. I think the main idea in the film was that Rebel sensors could detect big blips in Hoth orbit, like a massed fleet of big ships appearing out of nowhere at great speed, but cannot detect a smaller vessel like the Imperial probe droid.

It's also implied that maintaining the planetary shield around the Rebel base is both costly in energy consumption and could compromise the secrecy of the base by emitting a big radiation signature. Hence the Rebels don't simply keep the shield up permanently.

Answer 3

Simply put, it's to make a surprise attack.

If we look at the events, we can see earlier that the empire had no problem landing a probe droid nearby the rebel base. Had the empire been able to jump in outside of rebel sensors, they could have easily launched a strike force right on top of the rebels. Even worse, the empire could potentially have weapons that could cover that great distance (though this is theory as it is never demonstrated).

Instead, the fleet jumps in and this immediately triggers the rebel sensors. The rebels put up a large shield capable of handling extreme bombardment, and prevents the empire from landing any troops near the rebel base. Now the empire is forced to land troops much further away to attack the rebel base with their version of tanks.

Now remember why the empire is attacking hoth. They aren't simply trying to scare the rebels away, but rather they want to stomp out any rebellion they can. Had they gotten the element of surprise, they could have potentially captured or killed everyone on the Hoth planet. That includes all of the ships that escaped, any important figure heads, as well as the people directly responsible for the destruction of the Death Star.

Instead they are detected, and treated to delay after delay. By the time they manage to get control of the base, anyone important has already left. Now that's quite the change in outcome, isn't it?

Answer 4

A key question may be whether energy weapons (or missiles) could be directed accurately at the rebel base from outside the range at which ships can be detected. If they could be, this offers a potential explanation for Vader's strategy, or at least one aspect of it.

Imagine that I am able to hyperspace into the system outside of ship detection range, and also have energy weapons (or fast missiles) that I can aim at the rebel base. By launching a fast-moving salvo of projectiles at the rebel base, it could be that I could hit vital targets on the surface of the planet before the enemy had time to spot or react to the incoming ordnance, especially with the asteroids in the system making detection even harder. (Perhaps the energy shield takes a non-trivial time to fire up.) The ideal target would of course be the shield generator itself: an early hit on that would have rendered the rebels helpless in the face of the surprise attack.

Veers makes immediate mention of bombardment not being possible, which suggests that it might have been the key plan, although it's also possible that he is simply mentioning this to explain the tactics that are and are not still on the table.

One other possible factor: it might have been that Vader's abilities with the force could have allowed for accurate sensing of ground targets in a way that most military planners would have assumed impossible. Therefore it could have been that Ozzel didn't even consider accurate long-range bombardment a viable option when Vader's abilities in fact would have made it a realistic possibility.

Answer 5

I will guess that it's because the jump happens within sensor range (or too close to the outer limit) and thus the rebels detected 1) the hyperspace disturbance of an entire fleet coming out of it and 2) the same fleet (and considering it's made of about a dozen Star Destroyers and the "Executor", it's not going to pass as meteors in no way).

Even without this, there is also the possibility that the moment they came out of hyperspace the Rebels would have a ship in orbit which could have given out the alarm and start shooting (and surely would have been destroyed, yet it's an annoyance better off not having).

And lastly, it's Vader's orders that were violated by a gung-ho captain. Wouldn't have mattered if it was the position of the fleet's exit vector from hyperspace or the temperature of his tea-if Vader tells you to do something and is specific on his instructions, you better damn do them just as he told them or start making peace with whatever you believe in.

Answer 6

What's fun to consider here is that some sensors would be lightspeed and some capable of looking into hyperspace. It's likely that coming out of hyperspace close enough to a target would allow the target to detect a hyperspace signal (instantaneously), but there is a distance where that signal would be too weak to pick up. Thus, I could come out of hyperspace at a distance where you can't notice over hyperspace, and where you'll also not notice me over radio or light for (say) several hours. I could then use this time to recon via optics: I could precisely know your orbit and build a partial map of your planet so that when I do make my final jump, I'll know exactly where to drop out and have solutions loaded into my big guns.

Dropping out straightaway could be a problem if I don't know the system ahead of time--which the empire doesn't because it's the type of unmapped place where rebels would hide.

I'll also mention Return of the Jedi, when Lando mentions "my friend's down there" right before they jump "down" into the the vicinity of Endor. This would seem to indicate that the rebels were massed near the system, so that "down" is closer to the nearest largest center of gravity, yet they were not yet detected by the imperials. They staged just outside of hyperspace-jump-burst-detectability, but near enough so that invaluable hi-res (km-pixel or meter-pixel instead of 1000km-pixel) and recent (hours old instead of weeks old) optical observation could be made.

This pattern reminds me of the BSG reboot jump clock episode, but not quite. You drop near (but not too near) your opponent (say, again, several light-hours), and observe the target and plan your final attack jump furiously before those several hours are over and they quite literally see you.