Welcome to netnexus.com

Corporal rank is currently kind of hard to push through if you don't know what you're doing with the banking because of some balance issues.

1) Dragoons start showing up, and can't be beaten usually. Wounded ones too.
2) Zealots don't show up till lieutenant, even tho they're way weaker then dragoons.
3) Zerglings just gone
4) Mutalisks too strong for corporal hp/equipment

You're basically kinda forced to farm hydralisks and sometimes overlords.
The only effective strategy is to just bank money, die, and promote through, to get more hp by promotions.

Some other issues:
Item drops don't start till around lieutenant range? Maybe turn them on earlier. It makes the stims more useful. Maybe let the stims be used automatically if you use until death to maybe save you. As they are now, only kinda used outside combat, because using attack instead of until death takes forever. But by the time you find them, you have way more hp then what they recover. Could also consider it being %hp based instead of flat?

Commander rank you start fighting overminds and rouge battlecruisers. Pretty much have to run from overminds, and battlecruisers aren't worth the hp loss to fight, mainly because there's like no good anti air weapons < 9.5m credts to buy. Probably ok to leave it as is, since have to run from things sometimes makes it sorta interesting player choice, so they can't just yolo click forever.

Siege tank armor (45) is just worse then Lv3 Energy shield in almost all instances. The 1/2 dmg reduction with shields scales infinitely with dmg and rank. Maybe buff the flat armors?