Russia is building its first dedicated “stealth” warship, but just how stealthy is it?

Russian state news outlet RIA Novosti reported earlier this week that Russia’s shipbuilding industry is forging ahead with the construction of the Project 20386 Mercury corvette class.

Although formally classified as a “corvette,” the Mercury-class is arguably closer to a frigate in weight, size, and capabilities. The Mercury ships are larger and heavier than the Steregushchiy class “corvettes” that they are replacing; the latter is already regarded as frigates by NATO.

The new warship is expected to field many of Russia’s latest weapons, including the Paket-NK torpedo system. The corvette is likewise expected to use Kalibr and Oniks cruise missiles, as well as certain types of surface to air missile and artillery systems. It has been speculated that the corvette will join Russia’s other modernized ships in supporting the 3M22 Tsirkon winged, anti-ship hypersonic cruise missile, though the full extent of its weapons suite remains unclear.

The new corvette is the latest in Russia’s ongoing naval modernization strategy of jettisoning parts of its bloated Soviet inheritance in favor of a small, but advanced local defense force. The project is widely described, both by western and Russian sources, as the first Russian warship built from the ground up around the concept of stealth performance. The flagship Project 20386 corvette, Merkuriy, was launched earlier this year and is expected to be handed over to the Northern or Black Sea Fleet in 2022.

The Mercury class is being built with composite materials and radar-absorbent coating, two design features commonly used to reduce observability; it will also feature a bespoke, stealth-oriented hull aimed at minimizing protrusions and slits. “The Mercury corvette will be Russia’s first Naval ship to receive radar-absorbent coating throughout its entire outer surface area. According to preliminary estimates, the 100-meter corvette will reflect radio signals in similar fashion to that of a small boat,” an insider source told RIA Novosti.

So, is the Mercury-class really Russia’s first stealth vessel?

It is important to understand that “stealth” doesn’t function like an ‘on’ or ‘off’ switch— it is not and has never been, a binary design choice that’s either present or missing. Rather, “stealth” refers to a wide spectrum of tools and approaches aimed at making an object harder to detect. As with most aspects of hardware engineering, there are always trade-offs to be made; choices made to minimize a weapon’s detectability may come at the expense of other performance categories like speed or armament loadout.

The Mercury class is most certainly not the first Russian ship to focus on incorporating stealth concepts. It was only several years ago that Russia’s new Admiral Gorshkov class was labeled as a “stealth frigate” by defense observers. Project 20386’s Steregushchiy-class predecessor,  which was also widely called a “stealth corvette,” already took significant steps to reduce radar and acoustic signatures.

The Mercury corvette, then, is the next major evolution of the Steregushchiy-class design, making tweaks and introducing new features to further reduce the ship’s detectability. The new corvette may very well be Russia’s stealthiest surface ship yet, but it is not a principally new kind of vessel.

Mark Episkopos is a national security reporter for The National Interest.