If by "we" you mean Russia, then yes, you have mobile missiles. America's mobile missiles glide quietly under the ocean in Trident nuclear submarines. All of America's land based launch capabilities are in fixed nuclear silos. They are not and have never been hidden; Russia even gets to come inspect them from time to time (and visa versa) as part of the treaties both nations have signed. Both nations maintain enough weaponry to launch a massive retaliatory strike even if hit with a first strike, it's part of what makes both nations feel secure that neither would be dumb enough to try a sneak attack. For America, some of the silos are placed far north in Montana to make an offensive first strike more effective, some of them are placed further south (Wyoming, Colorado, Nebraska) to give a few more minutes to get missiles off during a surprise attack. The silos are spaced out enough that each would require a ground burst to destroy them, but close enough so that the nuclear debris cloud (mushroom cloud) would potentially damage or destroy incoming warheads (coming in at ludicrous speed) before they made it to the ground. The radioactive cloud that would be farted into the upper atmosphere by the debris clouds from the attacks on these missile fields would probably be responsible for well over half the national fatalities in a counterforce nuclear attack. We're talking hundreds of near-megaton ground bursts.