[##:##] Command : harden <PLANES> <LEVEL>
The harden command is used to install missiles into protective silos which can prevent their destruction during a nuclear or non-nuclear attack. Each successive harden command will add to the current hardness level of the missile in question.
Each point of hardening uses one unit of heavy construction materials, and costs $5.
Once a missile has been placed in a silo (hardened to a level greater than 0) it can no longer be moved.
See also : launch , Nuke-types , Plane-types , Planes , Nukes