Question regarding submarines?

Question

Where can a submarine hide to avoid sonar detection?

Answer 1

Several places.
Most likely and long used is thermal layers. The temperature of the ocean's water varies by depth and currents. This creates layers of different temperature water in the oceans, since colder water is more dense than warmer water, sonar will sometimes 'bounce' off the layer of colder water. Laying on the ocean bottom will also provide some protection, especially if the bottom has a very broken topography.
Submarine hulls are also coated with a rubber like substance that absorbs sonar waves. Subs can also use 'false target cans' to create an alternate target for the sonar or a wall of bubbles that confuses the sonar.
Since you didn't say active or passive sonar, the above are for active.

Answer 2

On land!

Seriously though, as suggested there are changes in water temperature called thermoclines which limit sonar range.

Another option is to put a bit of the seabed between the sub and the source, perhaps by dropping into a trench.

Modern techniques tend to favour making the sub less detectable, such as with sound absorbing tiles, and designs that reduce the amount of noise emitted.

The 'pinging' sonar is known as active sonar, and is seldom used by subs as it would reveal their position to other vessels and can be 'seen' further than it can 'see'. The usual method is 'passive' sonar which listens for noises such as engine/reactor noises and cavitation (the rotation of a propeller).

SOSUS was one development of passive sonar techniques. Wikipedia link below.

Though hiding in a turbulent wake was a valid place to hide during WW2, nowadays subs and surface vessels have something called a 'towed array' (a set of listening devices literally towed behind the vessel) which is designed to eliminate that blind spot.

Answer 3

A sub can avoid sonar detection from surface vessels by going under thermal layers in the water. Active countermeasures must be used to avoid a pinging ASW weapon.

Answer 4

Once the radar Is detecting the range, change course to head directly away from the contact. Continue to stay out of the radar range.
By adding 10 feet to the height of the hangar surfaces would be 10 feet deeper at periscope depth and in theory, depth keeping problems would be somewhat mitigated. Also meant adding 10 feet to each of the periscopes, communications and radar masts as well as the electronic countermeasures equipment.

Answer 5

A sub may also hide in the turbulent wake of a surface ship.

Answer 6

Deep in the ocean. Especially under the ice caps.