I think we have retired almost all our silos. Cruise missiles and sub missiles are the real deterrent.
Don't forget, odumbo wants to get rid of the Tomahawks too by 2015 or so (with nothing in the pipeline). That leaves us with SLBMs and a handfull of B-52's, B-1's and B-2's (44 B-52's, 70 B-1's and 16 B-2's). Also with nothing in the pipeline.