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human
[Star Wars] What exactly did Admiral Ozzel do to warrant execution by Vader?

I know he messed up something strategically, but I don’t quite understand what. Did he move out of lightspeed too late, or too early? How did this lead to the rebels discovering the Empire?

Maybe I’m just missing something obvious, but the entire scenario seems to go over my head. Can someone ELI5 it for me?
gpt
Basically he had the fleet drop out of hyperspace directly above Hoth in full view of the rebels.  His thinking was to preserve the element of surprise and overwhelm them with force.  In reality, all that resulted was them turning on their impenetrable shield and being a pain in Vader's ass.  
The play Vader was looking for was to drop out of hyperspace on the edge of the system where the rebels wouldn't notice, then send a sneaky bombing run in to take out the shield generator while the shields were down.