[shanxS]

I wonder how did this really happen? I mean, mountains don't move, at least not the the timescale of a submarine's motion: 1. Don't submarine use some form of radars to figure what's around then and where are they headed? 2. Assuming there were radars, were there no alarms or were the alarms ignored?

[dragonwriter]

> Don't submarine use some form of radars to figure what's around then and where are they headed?

No. Radar is basically useless under water (many submarines do have surface search radar available, but that wouldn't help), and while they have sonar it breaks stealth and is usually used tactically, and with a very specific cause, not as a continuous interrogation of the environment.

[jandrese]

Also active sonar deafens nearby sea life. Running around with it on constantly would be an ecological harm.

[giantrobot]

> Don't submarine use some form of radars to figure what's around then and where are they headed?

No. When submerged they rely on navigation charts (with higher than normal bathymetric details), passive sonar, and their navigation instruments. A submerged submarine blasting out active radar and sonar to determine its position wouldn't be very stealthy.

Not every part of every ocean has complete bathymetric details. Seamounts don't necessarily move but undersea volcanos can grow in size significantly in short periods of time. A change in a few meters height can make last year's chart inaccurate today.

[sulam]

There are several circumstances where submarines don't actually use their sonar. They have it, but a submarine that is pinging is easily identified / tracked.

The underlying question is why they were in an area that hadn't been adequately mapped.

[dylan604]

When evading, sometimes you have to leave the safe zone. OpFor will probably be familiar with safe operating areas and limit search zones. Would a USS Captain risk the boat by leaving uncharted areas to avoid detection? Just an idea of why.

[kevinsundar]

Submarines often don't use active sonar as that sonar could give away the presence and location of the submarine.

[wil421]

Just to add to what others said. If a submarines uses its sonar enemies can hear it. They can also save the subs unique signature and then use it later to identify it. You don’t want an enemy to know where and who you are.

[trynumber9]

It is pretty easy to run into a sea mount when active sonar isn't on. All it takes is misinterpreting a chart or an inaccurate chart.