The Paltus-class submarine is the NATO reporting name for Russia's Project 18511 Halibut nuclear-powered special-purpose deep-water station family. Open sources describe two boats, AS-21 and AS-35, as improved follow-ons to the Project 1851 X-Ray/Nelma design, built at the Leningrad/Admiralty yard for carrier-borne deep-sea missions, diver-support work, and GUGI-linked seabed operations; published dimensions vary widely because the class remains highly opaque.
RUSI and specialist references place Paltus among Russia's GUGI-linked special-purpose submarines for seabed warfare and deep-sea work, but public sources do not tie AS-21 or AS-35 to one named modern conflict; the entry therefore remains in the editorial 2015 Various Conflicts bucket.
The Paltus boats sit in the Russian nuclear deep-water station line rather than in the normal attack-submarine force. Public sources describe Project 18511 as the improved two-boat Halibut/Paltus follow-on to Project 1851 X-Ray/Nelma, carried to operating areas by larger host submarines for deep-sea tasks.
| Element | Documented context | Catalog note |
|---|---|---|
| Project family | One Project 1851 AS-23 boat was followed by Project 18511 AS-21 and AS-35. | The page links the parent X-Ray/Nelma record because sources treat the three boats as a closely related family. |
| Carrier concept | GlobalSecurity describes the AGS as part of a complex using modified nuclear-submarine carriers and crew transfer through a transition compartment. | This supports carrier-borne deep-sea operation, but not a specific host submarine for every Paltus sortie. |
| Mission equipment | References describe pressure-chamber/diver-support equipment, manipulator arms or grabbers, and special deep-sea devices. | Open sources support seabed-work capability while leaving many payload and sensor details classified or disputed. |
| Conflict attribution | RUSI places Paltus within GUGI's seabed-warfare capability set. | No public source found in this pass identifies AS-21 or AS-35 in a named war, strike, or loss event. |
Project 18511 Halibut/Paltus was the two-boat follow-on to the earlier Project 1851 X-Ray/Nelma deep-water station; open sources often discuss all three boats as one Project 1851/18511 family.
| Variant | Configuration | Designation notes |
|---|---|---|
 | Predecessor deep-water station | The single AS-23 Project 1851 boat preceded the two improved Project 18511 Halibut/Paltus units and is usually treated as the parent X-Ray/Nelma family. Sources: Project 678 / Project 1851 - Nelma class / X-Ray class, Deep-diving nuclear-powered stations - Project 1851 |
| AS-21 | First Project 18511 boat | RussianShips and GlobalSecurity list AS-21 as the first Project 18511 unit, laid down in 1984, launched in 1991, and accepted into Northern Fleet special-submarine service in December 1991. Sources: Project 678 / Project 1851 - Nelma class / X-Ray class, Deep-diving nuclear-powered stations - Project 1851 |
| AS-35 | Second Project 18511 boat | Open references identify AS-35 as the second Paltus boat, built as yard number 01431, launched in 1994, and commissioned in 1995; RussianShips also reports later repair planning and a Gneys-4K1 sonar addition. Sources: Project 678 / Project 1851 - Nelma class / X-Ray class, Deep-diving nuclear-powered stations - Project 1851 |
GlobalSecurity records AS-21 as the first Paltus boat to be incorporated into the program, before its 1991 launch and commission.
Sources: Project 678 / Project 1851 - Nelma class / X-Ray class
AS-21 came into operation in late 1991, giving the Project 1851.1 family its first active boat.
Sources: Project 678 / Project 1851 - Nelma class / X-Ray class
The second Paltus boat, AS-35, entered operation in 1995 and completed the two-boat class described by open sources.
Sources: Project 678 / Project 1851 - Nelma class / X-Ray class
A recent seabed-warfare study and RUSI commentary still list Paltus among Russia's special-purpose submarines used for undersea infrastructure and special-mission work.
Sources: Towards “Operation Ivy Bells 2.0”, Stalking the Seabed: How Russia Targets Critical Undersea Infrastructure
