Missiles cost 4 turns to build and 4 turns to launch. To launch a missile you also need missile power. The Maximum is 75% which gives you the 100% of the accuracy you would get according to your research, but you can also fire at an reduced amount of power (as low as 30%). The new accuracy of your missile would be described as "Your actual accuracy = The accuracy you researched * (Missile power / 75)"

Missile Type Cost Attack Attacks
Nuclear Missile $100 000 500 000 S A V I B
Chemical Missile $35 000 250 000 S A V
Biochemical Missile $30 000 200 000 I
EMP Missile $20 000 0 20% power

The EMP missile does no actual damage but instead disables 20% of the enemy's power. Each person can have no more than 75% of their province's power disabled by EMP attacks.