STORY: From a trench near the front line in Ukraine's eastern Donetsk region, this 55-year-old soldier, who goes by the call sign "Dad," is conducting battleground training.
Ukrainian forces, now 27 months into a war with Russia, have become heavily reliant on older soldiers like "Dad" to defend the country.
But they need reinforcements.
33rd Mechanized Brigade chief sergeant, call sign Deputy, is 44 years old.
"In reality the average age of our brigade's soldiers is quite high - there are a lot of people over 50. But their motivation is much higher than of the young troops. They understand why they're here: for the sake of their kids and grandchildren. They understand that there is no one else to do it except us."
As fewer volunteers line up to fight for their country than in the first months of the war, Ukraine is now under pressure to call up more troops.
Call sign Canada, is a 40 year-old commander in the brigade:
"Older troops could be trained to hold defensive positions. But if it's about performing other combat duties - assaulting fields, trenches, returning our land - then of course we need younger boys who are more resilient."
Russia, having seized the initiative after a failed Ukrainian counteroffensive last year, is gradually making inroads that could threaten key cities and roads in the east.
This comes as Ukrainian officials say they want a full withdrawal of Russian troops and to regain all of their internationally recognized territory, a task many experts say will be difficult as the war grinds on and saps more resources.
Aimed at attracting more volunteers, Ukraine's call-up effort - bolstered by government and military PR campaigns - have offered candidates a choice of where and how to serve.
50-year-old Ukrainian soldier "Bell" had this appeal to compatriots:
"I don't judge (those who do not join the army). No one should be forced to join the army. They should understand that no one other than us and them will do this. This is important. Everyone will have kids and families at some point. They need to be defended now, not whenever you're given a draft notice."
