The Russian military claims that its submarines are undetectable because they have incorporated a number of stealth features, such as:

• Reduced noise emissions. Submarines generate noise from their engines, propellers, and other components. The quieter a submarine is, the harder it is to detect. Russian submarines have been designed with a number of features to reduce noise, such as using rubber mounts for the engines and propellers, and installing sound-absorbing materials throughout the hull.
• Advanced sonar. Submarines use sonar to detect other ships and submarines. Russian submarines have some of the most advanced sonar systems in the world, which can detect other ships and submarines at long ranges.
• Maneuverability. Submarines can be difficult to track if they are able to maneuver quickly and unpredictably. Russian submarines are equipped with advanced propulsion systems that allow them to do this.

It is important to note that no submarine is truly undetectable. However, the Russian military's claims about the stealth of its submarines suggest that they are some of the most difficult to detect in the world. This could give Russia a significant advantage in any future conflict.

In addition to the technical factors mentioned above, the Russian military's claims about the stealth of its submarines may also be motivated by psychological factors. By claiming that its submarines are undetectable, the Russian military may be trying to deter potential adversaries from attacking them. This is a common tactic used by militaries around the world.

Ultimately, the true stealth capabilities of Russian submarines are unknown. However, the claims made by the Russian military suggest that they are some of the most difficult to detect in the world. This could give Russia a significant advantage in any future conflict.