Commander's Challenge

You only need to complete 10 of the 50 missions and they do not need to be completed under par time. The below videos should at least give you clues as to how to go about it. Use the completion gauge on the world map to see how far you are - at 20% (with 2% gained per mission), you'll unlock this achievement

Taken from this post at x360a, and subsequently from Youtube, below are all 50 missions completed under par time. Although it's the PC version of the game, most are completed way under par time and so essentially the tactics remain the same with a little leeway for the slower Xbox controls.

http://www.xbox360achievements.org/forum/showthread.php?t=23...

Credit to CrazyOneRA3 for the videos and tarekegypt for repackaging the links into an easy to use list.

No Place To Hide
http://www.youtube.com/user/CrazyOneRA3#p/u/0/ETE08vQmQhw

The Omega Program
http://www.youtube.com/user/CrazyOneRA3#p/u/1/Ew5wuXBi7hE

No Match for the Guardian
http://www.youtube.com/user/CrazyOneRA3#p/u/2/CW3RJkXf8ac

Caught in The Cross Fire
http://www.youtube.com/user/CrazyOneRA3#p/u/3/oLJ7lfariTQ

Symphony of Steel
http://www.youtube.com/user/CrazyOneRA3#p/u/4/xtQSaJehl9w

Red Crush
http://www.youtube.com/user/CrazyOneRA3#p/u/5/CuzgF6oh9Ls

Kill-A-Ton
http://www.youtube.com/user/CrazyOneRA3#p/u/6/31ELQA_u_XY

Crate and Red Barrel
http://www.youtube.com/user/CrazyOneRA3#p/u/7/gAm9HupeWM4

King of The Monsters
http://www.youtube.com/user/CrazyOneRA3#p/u/8/dmdDwfniaBU

Creeping Death
http://www.youtube.com/user/CrazyOneRA3#p/u/9/ArVPV1SzYtA

Are You Experienced
http://www.youtube.com/user/CrazyOneRA3#p/u/10/7ocAAWTMbEc

Reap What You Sow
http://www.youtube.com/user/CrazyOneRA3#p/u/11/xvXGn6ufDY4

Dead Meat
http://www.youtube.com/user/CrazyOneRA3#p/u/12/2bvp_2bV0tk

All Guns Blazing
http://www.youtube.com/user/CrazyOneRA3#p/u/14/pn1N6KsmydI

Cat Fight
http://www.youtube.com/user/CrazyOneRA3#p/u/15/-c3-tzQgpZE

Ready To Roll Out
http://www.youtube.com/user/CrazyOneRA3#p/u/16/VzXx20AWvww

Robots and Ninjas
http://www.youtube.com/user/CrazyOneRA3#p/u/17/8WYPHzgRKRc

No Place to Hide
http://www.youtube.com/user/CrazyOneRA3#p/u/18/TQoDWI1FhCo

Behind The Iron Curtain
http://www.youtube.com/user/CrazyOneRA3#p/u/20/aYuncotAacg

Offshore Killing
http://www.youtube.com/user/CrazyOneRA3#p/u/21/zFdgpfKYL80

Number One Threat To America
http://www.youtube.com/user/CrazyOneRA3#p/u/22/REz0eFHinjk

The Final Countdown
http://www.youtube.com/user/CrazyOneRA3#p/u/23/UX_uhBPBCZw

High-Water Mark
http://www.youtube.com/user/CrazyOneRA3#p/u/24/FQmdLY9tu30

Blood Feud
http://www.youtube.com/user/CrazyOneRA3#p/u/25/a6aMdKzVv90

Battle Royale
http://www.youtube.com/user/CrazyOneRA3#p/u/26/5CxZehs-Q0Q

Future Warfare
http://www.youtube.com/user/CrazyOneRA3#p/u/27/5CH5Kgwz7n0

Athena's Wrath
http://www.youtube.com/user/CrazyOneRA3#p/u/28/zpvGAlc8nSo

The Omega Program
http://www.youtube.com/user/CrazyOneRA3#p/u/29/z-etJUruCRY

Defense of the Archipelago
http://www.youtube.com/user/CrazyOneRA3#p/u/30/R2b-hzLE_kM

Dirty Tricks
http://www.youtube.com/user/CrazyOneRA3#p/u/31/FCgozliI6Vg

Vicious Circle
http://www.youtube.com/user/CrazyOneRA3#p/u/32/9_BllFu_NKc

Tesla's Castle
http://www.youtube.com/user/CrazyOneRA3#p/u/33/9tTVUQjfxX8

Show of Force
http://www.youtube.com/user/CrazyOneRA3#p/u/34/696poIMFQzw

Double Barreled
http://www.youtube.com/user/CrazyOneRA3#p/u/35/cCJS10JcxSs

Chrono You Didnt
http://www.youtube.com/user/CrazyOneRA3#p/u/36/JuPqd47mN4Q

Fury Of The Empire
http://www.youtube.com/user/CrazyOneRA3#p/u/37/tKtwOtFCDyY

Arms Race
http://www.youtube.com/user/CrazyOneRA3#p/u/38/XD7BOT0Ec3Y

Dangerous Skies
http://www.youtube.com/user/CrazyOneRA3#p/u/39/wzle-HdZHiE

Out Of The Blue
http://www.youtube.com/user/CrazyOneRA3#p/u/40/ec5JL78efMA

Shrink Zone
http://www.youtube.com/user/CrazyOneRA3#p/u/41/OK-tUipApgs

High Seas Duel
http://www.youtube.com/user/CrazyOneRA3#p/u/42/6JP4JhFbBL8

Ice Breaker
http://www.youtube.com/user/CrazyOneRA3#p/u/43/bYrRbUpCv2Q

Battle Room
http://www.youtube.com/user/CrazyOneRA3#p/u/44/qGeCDji20Pw

Superb Commander
http://www.youtube.com/user/CrazyOneRA3#p/u/45/NvJkAawba48

Come And Get It
http://www.youtube.com/user/CrazyOneRA3#p/u/46/kgKPmIQX8cc

Scavenger
http://www.youtube.com/user/CrazyOneRA3#p/u/47/vA9BXmldtDM

The Motherland
http://www.youtube.com/user/CrazyOneRA3#p/u/48/MR4TOHMN8lc

Where Satelites Go To Die
http://www.youtube.com/user/CrazyOneRA3#p/u/49/B9Pq_RGfknk

Two Sides of Everything
http://www.youtube.com/user/CrazyOneRA3#p/u/50/Y1pTvriAIDk

Future Warfare
http://www.youtube.com/user/CrazyOneRA3#p/u/51/0jSpdVzqTmU

Be Quick or Be Dead
http://www.youtube.com/user/CrazyOneRA3#p/u/52/U1o0MEz8peY

Your Gold Mine Has Collapsed
http://www.youtube.com/user/CrazyOneRA3#p/u/53/eAcCA7a16Tg