The BBC has confirmed that the number of military casualties from Russia in Ukraine has exceeded 50,000. Over the second year of conflict, during which Moscow implemented its "meat grinder" strategy, the death toll rose by nearly 25% compared to the previous year.

Since February 2022, BBC Russian, along with the independent media group Mediazona and volunteers, has been meticulously tracking these fatalities.

The identification of many fallen soldiers has been aided by the discovery of new graves in cemeteries. Furthermore, our teams have diligently sifted through various sources such as official reports, newspapers, and social media to compile this data.

Our findings indicate that over 27,300 Russian soldiers lost their lives in the second year of combat, underscoring the immense human cost of territorial gains achieved through this conflict strategy.

Despite repeated attempts to obtain comment from Russian authorities, they have declined to provide any response. The term "meat grinder" has been used to describe Moscow's relentless tactic of continuously sending waves of soldiers forward to exhaust Ukrainian forces and reveal their positions to Russian artillery.

The total death toll of over 50,000 far surpasses the sole official acknowledgment of fatalities made by Moscow in September 2022, which stood at eight times lower. However, it's important to note that the actual number of Russian casualties is likely much higher. Notably, our analysis does not include the deaths of militia in Russian-occupied Donetsk and Luhansk, where fatalities would further increase the overall toll on the Russian side.

Meanwhile, Ukraine has been reticent in commenting on the scale of its own battlefield losses. While President Volodymyr Zelensky disclosed in February that 31,000 Ukrainian soldiers had been killed, estimates based on US intelligence suggest even greater losses.

The BBC and Mediazona's latest list of dead soldiers shows the stark human cost of Russia's changing front-line tactics.

The graph below shows how the Russian military suffered a sharp spike in the number of deaths in January 2023, as it began a large-scale offensive in the Donetsk region of Ukraine.

As Russians fought for the city of Vuhledar it used "ineffective human-wave style frontal assaults", according to the Institute for the Study of War (ISW).

"Challenging terrain, a lack of combat power, and failure to surprise Ukrainian forces", it said, led to little gains and high combat losses.

Another significant spike in the graph can be seen in spring 2023, during the battle for Bakhmut - when the mercenary group, Wagner, helped Russia capture the city.

Wagner's leader, Yevgeny Prigozhin, estimated his group's losses around that time to be 22,000.

Russia's capture of the eastern-Ukrainian city Avdiivka last autumn also led to another surge in military deaths.

Volunteers working with the BBC and Mediazona have been counting new military graves in 70 cemeteries across Russia since the war started.

Graveyards have been expanded significantly, aerial images show.

For example, these images of Bogorodskoye cemetery in Ryazan - to the south-east of Moscow - show a whole new section has appeared.

Pictures and videos taken on the ground suggest most of these new graves belong to soldiers and officers killed in Ukraine.

The BBC estimates at least two in five of Russia's dead fighters are people who had nothing to do with the country's military before the invasion.

At the start of the 2022 invasion, Russia was able to use its professional troops to conduct complicated military operations - explains Samuel Cranny-Evans of the Royal United Services Institute (Rusi).

But a lot of those experienced soldiers are now likely to be dead or wounded, says the defence analyst, and have been replaced by people with little training or military experience - such as volunteers, civilians and prisoners.

These people can't do what professional soldiers can do, explains Mr Cranny-Evans. "This means they have to do things that are a lot simpler tactically - which generally seems to be a forward assault onto Ukrainian positions with artillery support."

Prison recruits are crucial to the success of the meat grinder - and our analysis suggests they are now being killed quicker on the front line.

Moscow allowed leader Yevgeny Prigozhin to begin recruiting in prisons from June 2022. The inmates-turned-fighters then fought as part of a private army on behalf of the Russian government.

Wagner had a fearsome reputation for relentless fighting tactics and brutal internal discipline. Soldiers could be executed on the spot for retreating without orders.

The group continued to recruit prisoners until February 2023, when its relationship with Moscow began to sour. Since then, Russia's defence ministry has continued the same policy.

Prigozhin staged an aborted mutiny against Russia's armed forces in June last year - and tried to advance towards Moscow before agreeing to turn back. In August, he was killed in a plane crash.

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