Quote from : Star Wars: Episode V - The Empire Strikes Back Movie

Darth Vader: What is it, General?
General Veers: My Lord, the fleet has moved out of lightspeed. Com Scan has detected an energy field protecting an area of the sixth planet of the Hoth System. The field is strong enough to deflect any bombardment.
Darth Vader: The Rebels are alerted to our presence. Admiral Ozzel came out of lightspeed too close to the system.
General Veers: He felt surprise was wiser...
Darth Vader: He is as clumsy as he is stupid. General, prepare your troops for a surface attack.
General Veers: Yes, my Lord.