well Ill give you few more details,
at silo lvl 2 u can build APMs
at silo lvl 4 u can build IPMs
1 APM will counteract 1 IPM and each missile can be used only once!
For each lvl of rocket silo ull get 10 spaces and each APM takes 1 and each IPM takes 2
One IPM assuming an APM doesnt counteract it, will destroy 50+ rocket launchers, and defenses destroyed by IPMs dont reactivate.
You build your missiles on the Defense screen and they go in the queue like ships and defenses, hence if you have a ship building at the time, ur missile wont start building until you ships done, and vice versa
Missiles will require stuff to unlock them as well, eg. u have to have a shipyard, but its minimal so you will have unlocked them
IPMs have limited range, about 30 ss is what I remember but its been a while, so look that up if you are into IPMs
You dont need extra fuel to launch an IPM, you just need to build them
If you have anything more specific you wanna know, ask a more specific question