A long time ago in a galaxy far, far away...
In the Star Wars universe, a secret Rebel Alliance headquarters on the ice planet Hoth, carved out of interconnected ice caves. The largest cavern served as the main hangar for the Rebel transports and fighters. It was guarded by a large shield generator and a big ion cannon.
The Rebels were just in the process of settling into this new hideout at the start of Episode V: The Empire Strikes Back. In the opening scenes of the film, an Imperial Probe Droid impacts on the planet, mistaken for an asteroid impact by hero Luke Skywalker. The 'droid does not spot Luke, but does see the Rebellion's shield generator. It sends off a report to the Imperial task force searching for the rebels. Although the report is incomplete and is dismised as unimportant by Admiral Ozzel, he is overruled by Lord Darth Vader. Vader appears to sense the Rebel presence via the Force, and orders the Fleet to jump to the Hoth system.
Admiral Ozzel brings the fleet out of hyperspace too close to the system, alerting the Rebels to its presence. The Imperial forces are forced to make a ground assault, treating us to an epic (if silly) confrontation between the Rebel snowspeeder pilots and the armoured might of the Empire's elephantine AT-AT walkers.
"Echo Base,
Far away in time,
Echo Base,
Far away in time."
OR, wait, maybe that's Echo Beach by Martha and The Muffins. Sorry.