How to play Countermeasure on Mac

We've just received word that terrorists have seized one of our missile silo complexes and are threatening to blow up Washington, D.C. These lunatics aren't fooling! They've wired the missiles to a silo computer and started the launch sequence timer. In just 10 minutes the missiles will lift off for Washington... unless YOU stop them. Destroy all the silos in the complex with your long-range turret gun before the timer runs out. If you complete this mission, you'll win the Congressional Medal of Honor... along with 10,000 bonus points and a bonus life. If the timer runs out before you destroy all the silos, you still have a chance to prevent disaster. In the seconds before impact, dock your supertank at a silo, enter the War Room, and guess the fail-safe code that disarms the missiles: The code is some combination of the letters L, E, and O... for example, ELL, OOO, or OLE. Succeed and you win 10,000 bonus points and a bonus life. Fail and... well, you'll find out.