Russian President Vladimir Putin has ordered a partial mobilisation, with 300,000 reservists set to be called up as the war in Ukraine continues.
But what does this mean? What is Russia's reserve force and how does it work?
Firstly, the Russian military is made up of a hybrid system and is heavily reliant on conscripts for both its active military and reserve force.
After completing their mandatory service with the active Russian military, conscripts are then placed in Russia's reserves.
Russian conscripts, men aged 18-27, usually serve one year.
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Russia's reserve force - its size and strength
Russia has one of the biggest reserve forces in the world (more than double the size of America's) but how it is made up is very different to others.
It is reliant on former conscripts and veterans, although Russia in recent times has been trying to increase its number of volunteer reservists, similar to the systems used in the West.
The Institute for the Study of War says few are actively prepared for war, with only 10% of reservists undergoing refresher training following their initial service.
Lieutenant Colonel (Retired) Glen Grant, former advisor to the Ukrainian Ministry of Defence, told Forces News that Russia will be bringing in 300,000 "low grade" troops.
"It’s 300,000 people who don't want to go to war, there's not going to be any of them happy about going," he said.
"The Russian infantry is weak and bodies in infantry just means more dead bodies, because they are not going to have the skills for coordinated fighting any more than the ones they've got already.
"The ones they've got at the moment, all they're doing is just pushing them over the line, basically to die.
"They're not happy people, lots of them have lost their friends, lots of units have been destroyed and I suspect that by now much of the army understands it's a lost cause."
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Following Mr Putin's announcement, Russian defence minister Sergei Shoigu said only those with relevant combat and service experience would be mobilised.
The Institute for the Study of War reports current Russian laws limit the mobilisation of reserves to soldiers and sailors younger than 45 and officers younger than 55.
It also limits it to men who have been transferred to the reserves less than two years ago, with fathers of three or more children and those with a criminal record exempt too.
The tink tank added Russia has looked to create exclusively reservist units but likely failed due to low engagement.
Russia has suffered a number of losses in Ukraine in recent weeks, with Ukraine launching a successful lightning counter-attack.
Some believe Russia is exhausting its readily available manpower, with the reservist personnel being deployed straight to the frontline unlikely to be well-trained or motivated.
The Russians have given their first update on the official death toll since March this year, claiming 5,379 service personnel have been killed. Western sources put this figure almost three times higher.
Lt Col Grant said some of the Russian media has picked up on this, questioning the need for 300,000 more reservists.
The UK's Ministry of Defence (MOD) said on Wednesday that Russian forces "continue to experience personnel shortages", with a vote amending a law which extends punishments for defaulting troops - alongside the announcement of a reservist expansion.
"Putin is accepting greater political risk by undermining the fiction that Russia is neither in a war nor a national crisis in the hope of generating more combat power," the MOD tweeted.