Unlock higher ranks by earning more points and a higher "Difference" score.
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Corporal → 30 points, 30 difference, can create squad option

Sergeant → 100 point, 70 difference, can create clan option

Sergeant 1st Class → 200 points, 100 difference, unlocks Shotgun and SMG

Master Sergean → Master Sergeant: 350 points, 150 difference, unlocks the medic badge

Sergeant Major → 550 points, 250 difference, unlocks HGH and ISA LMG

Lieutenant → 880 points, 250 difference, unlocks engineer badge

Captain → 1100 points, 300 difference, unlocks VC9 missile launcher

Major → 1450 points, 350 difference, unlocks tactician badge

Lieutenant-Colonel → 1850 points, 400 difference, unlocks grenade launcher

Colonel → 2300 points, 450 difference, unlocks saboteur badge

General → 2800 points, 500 difference, unlocks scout badge