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Matthew Parker thought he would be in Ukraine by now, helping the country fight off invading Russian forces.
Instead, the US Army veteran is at home in South Carolina helping other veterans find their own way to the war-torn country.
Following the call, Ukrainian embassies around the world were inundated with offers from people looking to join the fight, with more than 20,000 having signed up so far, the country's defence ministry reported.
So many have inquired that applications have been limited to those with previous combat experience.
Mr Parker, who retired from the Army as a sergeant first class 10 years ago, has all the requisite combat experience after three tours in Iraq and a peacekeeping tour in Bosnia. And now he’s helping the Ukrainian embassy in Washington sift through applications.
“I am unofficially helping the Ukrainians vet people” said Mr Parker.
It's a long process. Veterans must first email the Ukrainian embassy in their respective countries then submit documents proving their identity and combat experience. If they successfully complete that stage, they are interviewed by an embassy official.
Mr Parker, who runs a security training company in South Carolina, is helping the embassy run background checks and conduct interviews with aspiring foreign soldiers.
“I've interviewed him about his experience to determine where he would be best be suited,” said Mr Parker of a recent veteran he spoke with.
“And I've already written a note, which I will attach to his application, that I'll tell the Ukrainians based on my background check and my interview with him, I believe him to be suitable and I've already sent a message that says there are his specific talents and this is what I think you should do with him.”
Many of the people looking to volunteer are veterans of the wars in Iraq and Afghanistan. But working for the US military is different from working under a foreign government under attack.
“The army always took care of everything, so to go over there on their own, it's a little different,” Mr Parker told The National.
Many of the veterans cannot afford their own body armor or plane tickets, so Mr Parker has helped some connect with donors who can provide airfare while working with vendors to track down less expensive equipment.
He is also helping to arrange transport from Poland to Ukraine, where soldiers will be met by representatives of the Ukrainian International Legion.
Once in Ukraine, the volunteer soldiers will sign their enlistment papers.
"Wali", a Canadian sniper who served several tours in Afghanistan, has been in Ukraine for more than a week.
He said the situation on the ground with so many foreign fighters arriving at once has been a bit “chaotic”.
The sniper, who asked only to be referred to by his combat name, is part of a group of foreign fighters called the Norman Brigade. He arrived before Mr Zelenzkyy’s appeal for help.
Wali said it took more than a week to reach the front line and he still hasn’t seen any combat.
“The logistics are a bit messed up,” he told The National by phone. “Because everything moves so fast.”
The 12-year military veteran said the experience reminds him of his time fighting alongside the Peshmerga in northern Iraq against ISIS.
“It looks like the experience I had with the Kurds,” he said. “It's not as simple as it looks. A lot of people think that you just land near Ukraine and somebody gives you a weapon right away with bullets and you just start shooting everywhere.”
But Wali said he’s still waiting to receive a sniper rifle. Despite this, he is confident he will see combat soon.
As to why he joined the war effort, he said he felt compelled to help defend Ukraine.
“The question that we should ask is what do the Ukrainian people want? They want to be like Europe. They don't want to be like Russia,” he said. "I think they should be left alone.”
Russian President Vladimir Putin’s assault on Ukraine has stirred many veterans to action, awakening a primal sense of right versus wrong and good versus evil.
“This is the line and these people need help and they're fighting to the death, and their force is doing what it can do, so if I have the means to help, I'm gonna go help,” said Ward Carroll, a retired US Navy fighter pilot.
Mr Carroll, who hosts a popular YouTube show that focuses on the military, said many veterans heading to the front will have already accepted the possibility of dying and feel that this is a “just” mission that provides them with the purpose and direction they've been lacking in their post-military lives.
That is the mindset of Clayton Vonderahe, a retired Marine Corps correspondent.
“All I do is install auto glass,” he said. “That's one of the reasons why this almost sounds appealing, is I really want to live a life of substance again.”
Mr Vonderahe has only recently begun the volunteer application process and has not yet heard back from the Ukrainian embassy in Washington.
For Mr Parker, who is helping the Ukrainians approve applications, the reason to help is simple.
“I don't like bullies,” he said.
Once he is no longer needed in the US, he plans on flying over to join the fight in person.