At the Battle of Hoth, the Imperials employed a great ground assault legion, dubbed Blizzard Force to capture and destroy the rebel fortress of Echo Base. The ruthless General Maximillian Veers lead the attack, and it was considered to be the Rebellion's worst rout during the Galactic Civil War.

Imperial Command

Darth Vader
General Maximillian Veers
Brigadier General Nevar
Colonel Starck

Imperial Force

Blizzard 1 - General Veers' AT-AT walker
Blizzard 2 - Brig. General Nevar's AT-AT walker
Blizzard 4 - Colonel Starck's AT-AT walker
Blizzard 6 - AT-AT walker
Blizzard 8 - AT-AT walker
Blizzard 9 - AT-AT walker
Blizzard Scout 1 - Lieutenant Arnet's AT-ST walker
Other AT-AT walkers
Other AT-ST walkers
AT-ARs
AT-PTs
Arakyd Viper Probe Droids

Imperial Casualties

Blizzard 1 - Disabled when Rogue 4, piloted by Derek "Hobbie" Klivian and Kesin Omiss collided with it's cockpit. Veers survived but was crippled. (ESB Novel)
Blizzard 2 - Destroyed by Rogue 3, piloted by Wedge Antilles and Wes Janson. They used their snowspeeders' tow cables to topple it. Nevar was killed. (ESB movie)
Blizzard 4 - Destroyed by Luke Skywalker, who was on foot and used a harpoon gun to hoist himself up into it's underbelly and cast a grenade inside. Starck was killed. (ESB movie)
AT-AT walker - Destroyed by Dash Rendar in Rogue 12. (SotE game)
AT-AT walker - Destroyed by Wedge & Janson in Rogue 3 (RL)
AT-AT walker - Destroyed by Wedge & Janson in Rogue 3 (RL)
AT-AT walker - Destroyed by Wedge & Janson in Rogue 3 (RL)
AT-AT walker - Destroyed by Luke on foot (RS)
Walker - Lost in Kerane Valley (SW-CL)
Walker - Lost in Kerane Valley (SW-CL)
Walker - Lost in Kerane Valley (SW-CL)
Numerous AT-STs - Destroyed by Luke and Wedge in Rogues 1 & 3 and Luke on foot (RSq/RL/RS)

I believe that the three walkers lost in the Kerane Valley were AT-ATs, and were Blizzards 3, 5 and 7. This leaves Blizzard 10 as the walker destroyed by Dash Rendar. I think that the other walkers destroyed in the Rogue Squadron series should not be really taken as canon, but some of the AT-STs that you destroy should be, such as those attacking Outpost Beta or that Luke destroys with the E-Web. This leaves around a dozen (3 with the E-Web, 9 at Outpost Beta) AT-STs that were destroyed. This means that there must be at least 15 AT-STs on Hoth. If there are 10 AT-ATs, there are also at least 10 AT-STs, as the Titan dropships carry four of both types of walker. The three destroyed by the E-Web came seperately, as do at least three attacking Outpost Beta. This gives us at least 16.

At least 10 AT-AT walkers (at least 7 destroyed)
At least 16 AT-ST walkers (at least 12 destroyed)

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Right, that's the Imps on Hoth sorted, tomorrow I'll list the Rebel forces present in the battle. If you have any comments, please let them be known!