telling them all but get out of the area. >> reporter: the defense secretary told the bbc u.s. ships are positioned, preparations complete. >> we are ready to go. >> reporter: and a defense official tells cnn if the president chooses the most limited option, it could be over in two to three days. cruise missiles could target syria's weapons launchers and command and control facilities, but that's it. >> the options we are considering are not about regime change. >> reporter: and this some say could backfire on the white house. >> it may give bashar al assad a propaganda advantage by saying he was able to resist the united states' attacks. >> reporter: the administration continues to accuse bashar al assad of gassing his own people. >> there is no doubt who is responsible for this heinous use of chemical weapons. >> reporter: but so far, they've offered no hard evidence. >> the intelligence community is working on an assessment. >> reporter: u.s. officials tell cnn that assessment includes forensic evidence that chemical