chance. david? >> rachel scott live in houston tonight. rachel, thank you. and i know rachel will have much more of her interview in a reporting project for "nightline" that will air next week. in the meantime here, we continue tonight and the u.s. navy now confirming the nuclear powered submarine, the uss connecticut, and a collision, striking an unknown object under water in the pacific. the boat now headed to port to assess the damage. we took you onboard a nuclear submarine in the med arbitrary yan this was two years ago, the uss florida. we saw that technology up close. we've saw how tell think these submarines are. wait to bring in martha raddatz, because martha, you've been on these submarines, as well. a lot of people at home are going to be asking, how does this happen, how does a collision even take place? >> reporter: david, we know these nuclear-powered attack submarines are all about stealth and in order to remain stealthy, the submarines will often turn off their act tive sew nor so ty can't be detected. so that leaves them blind,