I'd assume they were assuming a worst case scenario of something like a ballast malfunction paired with a propulsion malfunction, so you have a partially buoyant (enough to stay off the ground, not enough to surface) craft being pushed both by currents, and possibly its own propulsion, in an unknown direction in some radius outside of the Titanic. I've no idea of the depth sonar can accurately ping, so they may also have been considering the 3-d area around the Titanic in which case you're hitting radius cubed, and so even a "small" max distance could be huge.
Ever use a fish finder / depth finder? A narrow beam is sent in one direction, generally down, and reflections back are calculated. I would imagine that was the start of their search.
After enough time or support: military grade sonar? https://man.fas.org/dod-101/navy/docs/es310/SNR_PROP/snr_pro...
Yip, but the issue is the depth. The Titanic's at 3800 meters. An average military sub isn't going to hit 1000 meters. So I'm reluctant to make any assumptions about deep search systems.
Most work class ROVs top out around 3,000 meters but there are plenty of ultra-deepwater ROVs that go to 4,000 meters and beyond that are specialized for search and rescue operations. The usual ROV players like Oceaneering International, Saab SeaEye, TechnipFMC, etc. all make them.
The Navy & Coast Guard would definitely have access to their own fleets
I'd assume they were assuming a worst case scenario of something like a ballast malfunction paired with a propulsion malfunction, so you have a partially buoyant (enough to stay off the ground, not enough to surface) craft being pushed both by currents, and possibly its own propulsion, in an unknown direction in some radius outside of the Titanic. I've no idea of the depth sonar can accurately ping, so they may also have been considering the 3-d area around the Titanic in which case you're hitting radius cubed, and so even a "small" max distance could be huge.