Unlock all mechs & missions in Free Mission mode:

At the Title screen, switch the tuner to the following numbers and hold for one second each:

1-9-7-9-0-9-0-6

Position '0' is on the left end of the dial (9 o' clock position), position '4' is at the top of the dial (12 o' clock position) etc.

Movie viewer:

Beat the game on Normal difficulty. You'll find the Movie Viewer at the Configuration menu.

Voice select option:

Beat the game on Veteran difficulty. You'll find the Voice Select at the Configuration menu.

Desperado difficulty setting:

Beat the game on Veteran difficulty.

Lower mech:

Beat the game on Desperado difficulty. Press Hatch + Start during play to lower your mech.

Remove HUD:

Get rank of Lieutenant Colonel. Then, press Ignition + Start during play.

Juggernaut mech:

Get to rank to Colonel.

Rapier mech:

Get ten decorations.