cbs news national security correspondent david martin is at the pentagon. >> reporter: hundreds of new i.c.b.m. silos under construction. a massive buildup which has forced the pentagon to drastically revise the number of nuclear warheads china is adding to its arsenal. the commander of u.s. nuclear forces say it's a game changer. >> we are witnessing a strategic breakout by china. the explosive growth and modernization of its nuclear and conventional forces can only be what i describe as breathtaking. >> reporter: in a new report, the pentagon warns china could have 1,000 nuclear warheads by 2030, almost a five-fold increase over the current number. hans kristensen of the federation of american scientists has been monitoring the buildup. >> it's an astounding pace. >> reporter: have the chinese ever done anything like that before? >> it's far b eve in tcoul baded hypersonic missiles, which are harder to