The Yasen-class submarine is a new class of nuclear-powered attack submarine in service with the Russian Navy. It is designed to be more stealthy and maneuverable than previous classes of Russian submarines, and it is armed with a variety of new weapons systems. The Yasen-class submarine is one of the most advanced submarines in the world in service with the Russian Navy.

In the 1980s, Soviet navy started looking for a new SSN which would replace the Victors and counter the LA class. The LA was superior to Victor in almost all aspects. LA flight 2 fielded VLS cells which could the deploy sub launched variant of TLAM (Tomahawk Land Attack Missile) or TASM (Tomahawk Anti Ship Missile) providing a massive increase in capability for the USN. The Soviets needed an attack sub better than the LA to even the odds. Hence they officially started work on this new sub in 1986 which would be called as the Yasen.

K-329 Severodvinsk (Credits-On the pic)

USN started fielding the newer LA class SSNs in 1976 thus in 1977 Malachite design bureau started unofficial work on a new 4th gen SSN which would be a replacement for the  Victors, the then mainstay of the Soviet fleet. In 1986 work officially started on this new sub which was named as Project 885 Yasen, its NATO name hasnt been confirmed.

K-329 moving out of Sevmash for seatrials

This sub would displace slightly more than 9000 tonnes of water while on surface, with a length of 120m, submerged top speed in excess of 35kn and maximum diving depth of 600m.  She would be the first Russian sub to have spherical sonar array in the bow with 10 torpedo tubes speculated to be a mix of 533mm and 650mm placed amidships. She would carry 30 weapons internally and 32 missiles in 8 big silos which are quadpacked. These silos would carry the P-800 Onyx AShM to counter the advatage of sub launched TASM from LA flight 2. These subs from the onset were supposed to be quieter than the LA and thus making them a major threat for the allied navies. Like their predecessors they would carry a relatively small crew of 90 men including 32 officers compared to 120 of LA, 145 of Seawolf and 130 of Virginia. It also features 4 wide aperture arrays, two larger arrays on either side of bow and two smaller ones near the aft section.

Yankee Bignose, used to test Yasen’s spherical sonar array

Akula class which was developed as a replacement for the titanium hulled Sierra played an important role in development of the Yasen. Lead boat of the Akula class entered service in 1984 ie 2 years before Project 885 was officially started and it was evident from the first day that Akulas were good enough for the LA and hence Yasen was put on the back burner. The first vessel was laid down in 1993 ie 16 years after the programme was originally started. Cold war had ended by that time hence the production was stalled till early 2000s and the ship was launched in 2010 after nearly 17 years of construction. There were some changes in design over the years, K-329 we see today is 139m long instead of 120m which means it has a newer and quieter propulsion system (usually increase in length corresponds to quieter propulsion system for the Russians).

Shows K-329 is longer than what it was supposed to be.
(Credits-On the pic)

K-329 was inducted into the Russian navy in 2013, ie more than 2 decades after being laid. This mushroomed the costs and made it the costliest sub ever built along with the American Seawolf class. It still sported a conventional propeller instead of a pumpjet seen on most of the modern SSNs which made it more noisy at shallow depths than the comparable Seawolf. Hence the Russians decided against producing subs with the same config and the next sub ie K-561 Kazan sports several design changes and is called Yasen-M. Yasen-M is rumored to have 8 torpedo tubes instead of 10 whereas the number of missile silos is increased to 10. Originally, it was thought that the Kazan would have a pump jet propullsor but to our astonishment the boat was launched with a traditional propeller. Some were quick to point out that this makes the sub inferior to western boats with pump-jets. The Russians tested a Kilo fitted with a pump-jet to analyse its pros and cons came to the following conclusion.

1. Pump-jets are primarily used to reduce cavitation noises which are prominent during acceleration and deceleration.
2. Cavitation noise goes down as depth increases.
3. Russian boats traditionally operate at higher depths compared to western boats, a tactic usually used to get rid of trials during cold war.
4. Below 500m, there is virtually no cavitation even at high speeds.
5. Every pump-jet has an optimal speed for noise reduction, beyond which it acts like a resonance box thus limiting the range of possible speeds for a submarine.

Thus they don’t need pump as their overall design and capabilities take care of the requirement. The Boreis need them as they would need to operate near the surface for launching their ballistic missiles and hence Boreis have pump-jets while Kazan and the lead boat don’t. Interestingly Kazan is slight different from Severodvinsk. It is about 10m shorter which could be done by increasing automation thus reducing crew size.

The differences (Credits-On the pic)

Hence the sub originally envisioned to counter the LA will now replace the Akula, which ended up facing the LA. They would replace the Oscars as well. The Russians arel building 5 Yasen-Ms which are better and cheaper than the Yasens. The first of the follow-on class was launched on 31st of March 2017 i.e. years behind schedule. The other boats are progressing slowly as well. The Russians have started work on a new class of boats called Husky which might see fruition in the next decade or the decade after.

K-329 firing Kaliber missile

K-329 firing a salvo of 2 Onyx AShMs

Torpedo tubes of K-329

Displacement	~9000 tonnes
Length	139m
Beam	15m
Max Diving Depth	600m
Propulsion	OK-650 reactor driving a single propeller
Max Speed	~35kn
Crew	90
Armament	6x650mm and 2x533m torpedo tubes with 30 weapons carried internally, 8 silos which can be quadpacked
Weapons Carried	Type 65 torpedoes (probably phased out) Type 53 torpedoes Klub AshM Kaliber LACM P-800 AShM
Sonar Arrays	Spherical array in the bow 4 wide aperture arrays Single towed array