there are other similar vehicles with better depth capability. the rima 6,000 an autonomous underwater vehicle but can go . 3.7 miles down. the u.s. navy has those but deployed on military missions and not available. also this device called the orion, side scan sonar, it can go a mile deeper than the bluefin. only problem, knit a warehouse in maryland disassembled. >> it's ready and available but it has not been requested. >> reporter: so why haven't the search coordinators in australia asked for a vehicle which can go deeper, especially when there are part of the search area deeper than the bluefin's range. >> they haven't responded to that specific question from cnn. but have said this -- >> at the moment, it looks like the bluefin-21 is more than adequate for the task. >> reporter: but experts say, time is working against the search teams. no underwater audio signals have