> My phone can do "safety-of-ship" alerting? Yes. It's a very similar problem to aviation terrain avoidance systems which are now so common, and such a "solved

> My phone can do "safety-of-ship" alerting? Yes. It's a very similar problem to aviation terrain avoidance systems which are now so common, and such a "solved problem", that numerous popular smartphone apps for flying and gliding feature not only terrain warning but features like "will I be able to make it to that airport" determination (for gliders) which factors in a slew of real-time parameters and terrain data. And, really, "is the plane going to hit terrain the way it's being flown right now?" is far more complex than the problem the author was describing, which "is what you're planning to do going to hit terrain." They commanded a dive to a depth below the ocean floor, and it wasn't like they were trying to run a canyon like Hunt For the Red October...from the sounds of it, nothing in the area was deep enough to permit that dive to happen safely. This problem is also a problem the PC/console game development community solved, oh, around two decades ago. For quite some time games have simulated bullet physics while also determining if a shot hits a moving, deforming, 3d object, with checks happening in a matter of ~10ms or thereabouts. "Will the submarine pass within X feet of underwater terrain" is a walk in the park. There's also the matter of the system not needing to assure a maneuver is safe, but merely to serve as an alert when something is obviously not safe. Given how much these things cost, as you point out, I'd say such a system is beyond warranted. > Not only this but navigation information would have to be fused together from GPS as well as INS (inertial nav). I'm going to guess that the Navy has figured out how to very precisely geolocate their submarines and has beyond-excellent seafloor map data.