Another hint. (oh, brother, here we go again). When you've got many turrets, get to a safe-ish point and stop your turrets from firing (shift). Then, start them up (space) a second or two later. This makes all of the turrets fall in line, causing maximum devastation of the enemy fleet.
Have to get past lvl 1?
Priorities...
1. set up a decent angle on your turret.
2. get 3 stars on supply train
3. get 1 star on repairman
4. get 3 stars on recycler
5. 5 stars on supply train
6. 5 stars on recycler
7. get $6000 (not so hard now, huh)
8. mash buttons 2,3,4,5,6 on keyboard until out of money
9. watch you're fleet raze the enemy("raze"? look it up!)
10. bask in the glory of victory!
hint...
try to keep a helicopter, frigate, and sub (all with full health) on the board at all times.