Each nation has a secret superweapon that requires the following conditions to be met. The nation must control less than ten battlefields and have lost the battlefield, including the area where the weapon appears. They then must retake it and control the UW's battlefield when the area is retaken. The secret mission will be available for approximately an hour once those conditions have occurred. Complete the mission to unlock an achievement and 3,000 Valor experience points for all RTs. The superweapons and locations are as follows:

SUPERWEAPON - LOCATION
Sal Kar Ghalib - South Cemo Oil Fields, Gazi
Tarakia M-99 Patriot - Wakool, Balares
MorskojMSK-X0 - East Salma Woods, Xivera

To get infinite fuel for your Hound, choose a chassis with low energy usage. Choose a cockpit with low energy usage and high internal power. Do not add a fuel tank or generator and do not exceed your Hound's energy usage.

Leg Up training hint:
You can quit story mode anytime and participate in each story's tutorial to get a feel for each Role Type (or RT). If you do well, you also unlock the basic parts (bodies, legs, generators, and support) for those RTs as well, so can start designing your own Hound.

ACHIEVEMENT - HOW TO UNLOCK
Scout Complete (20 points) - Beat the Scout Arc in Story mode.
Soldier Complete (20 points) - Beat the Soldier Arc in Story mode.
Sniper Complete (20 points) - Beat the Sniper Arc in Story mode.
Gunner Complete (20 points) - Beat the H. Gunner Arc in Story mode.
Defense Complete (20 points) - Beat the Defender Arc in Story mode.
Command Complete (20 points) - Beat the Commander Arc in Story mode.
All Tact. Complete (20 points) - Beat all missions in Story mode.
Tact. Instructor (20 points) - Earn top marks in all Story mode missions.
Hover Specialist (20 points) - Deploy the Hover Chassis 50 times.
Wheel Specialist (20 points) - Deploy the Wheeled Chassis 50 times.
Biped Specialist (20 points) - Deploy the Bipedal Chassis 50 times.
Inverse Specialist (20 points) - Deploy on Inverse Chassis 50 times.
Tread Spec. (20 points) - Deploy on Treaded Chassis 50 times.
Multi Spec. (20 points) - Deploy on Multi Chassis 50 times.
Crushing Award (20 points) - Wipe out the enemy and live 100 times.
Storming Award (20 points) - Attack the opponent first 30 times.
Survival Award (20 points) - Return alive 10 or more times in a row.
Red Flag (20 points) - Win a total of 100 times or more.
Bronze Wing (20 points) - Destroy 50 or more enemy HOUNDs.
Bronze Flag (20 points) - Secure a COMBASs total of 100 times.
Bronze Hammer (20 points) - Destroy the enemy HQ and win 50 times.
Silver Wing (20 points) - Destroy a total of 100 enemy HOUNDs.
Silver Flag (20 points) - Secure COMBASs a total of 300 times.
Silver Hammer (20 points) - Destroy the enemy HQ and win 100 times.
Scout Valor (20 points) - Max your Scout experience level.
Soldier Valor (20 points) - Max your Soldier experience level.
Sniper Valor (20 points) - Max your Sniper experience level.
Command Valor (20 points) - Max your Commander experience level.
Gunner Valor (20 points) - Max your H. Gunner experience level.
Defense Valor (20 points) - Max your Defender experience level.
Bronze Patriot (20 points) - Stay with the same nation for 3 seasons.
Gold Eagle (20 points) - First in total fame for a given period.
Gold Cross (20 points) - First in seasonal fame at end.
Gold Wing (20 points) - First in average total fame for a given period.
Gold Hexagon (20 points) - First in average seasonal fame at end.
Gold Sword Cross (20 points) - First in total conquest points for period.
Gold Lion (20 points) - first in seasonal conquest points at end.
Marching Service (20 points) - Travel a total of 1000000.
Military Service (20 points) - Deploy total of at least 300 times.
Capital Occupation (20 points) - Affiliated nation destroys another.
Nation Resurrector (20 points) - Revive an affiliated nation.
Neroimus War Medal (40 points) - Affiliated nation wins Neroimus War.
Bloodless Award (20 points) - Win five times without attacking the enemy.
Combat Award (20 points) - Win ten times when outnumbered.
Dist. Service (20 points) - Destroy unidentified enemy weapon.
Humane Award (20 points) - End five times in a row without killing the enemy.
Silver Patriot (20 points) - Donate to affiliate nation once.
HOUND Specialist (20 Points) - Own one of each part.
Touring Service (20 points) - Deploy to every battlefield once.

Getting an A rank on any offline story mission will unlock a part. Get an S Rank in any offline story mission for either more parts or the S rank award. Note that a Hound that mixes RTs (soldier-sniper-defender) is better suited for early missions while a commander-heavy gunner is better for other missions.