Wired’s Danger Room blog has a detailed (read nerdgasm-inducing) breakdown of The Battle of Hoth from The Empire Strikes Back:
How did the Galactic Empire ever cement its hold on the Star Wars Universe? The war machine built by Emperor Palpatine and run by Darth Vader is a spectacularly bad fighting force, as evidenced by all of the pieces of Death Star littering space. But of all the Empire’s failures, none is a more spectacular military fiasco than the Battle of Hoth at the beginning of The Empire Strikes Back.
From a military perspective, Hoth should have been a total debacle for the Rebel Alliance. Overconfident that they can evade Imperial surveillance, they hole up on unforgiving frigid terrain at the far end of the cosmos. Huddled into the lone Echo Base are all their major players: politically crucial Princess Leia; ace pilot Han Solo; and their game-changer, Luke Skywalker, who isn’t even a Jedi yet.
The defenses the Alliance constructed on Hoth could not be more favorable to Vader if the villain constructed them himself. The single Rebel base (!) is defended by a few artillery pieces on its north slope, protecting its main power generator. An ion cannon is its main anti-aircraft/spacecraft defense. Its outermost perimeter defense is an energy shield that can deflect Imperial laser bombardment. But the shield has two huge flaws: It can’t stop an Imperial landing force from entering the atmosphere, and it can only open in a discrete place for a limited time so the Rebels’ Ion Cannon can protect an evacuation. In essence, the Rebels built a shield that can’t keep an invader out and complicates their own escape.
When Vader enters the Hoth System with the Imperial Fleet, he’s holding a winning hand. What follows next is a reminder of two military truths that apply in our own time and in our own galaxy: Don’t place unaccountable religious fanatics in wartime command, and never underestimate a hegemonic power’s ability to miscalculate against an insurgency.
Go read the whole thing — charts and maps and lot of good stuff applicable to warfare generally not just the film.