Marine 1st Lt. Hugh Conor McDowell was killed during a Camp Pendelton training exercise on May 9. He had been preparing to propose to his girlfriend, Kathleen Bourque. 

Theirs was a whirlwind romance, and it is a senseless tragedy that they will not get to build a life together. When he left for a 10-day training mission, Marine 1st Lt Hugh Conor McDowell, 24, told his mother that the ring he was having made out of two family heirlooms was nearly ready. 

With it, he was going to propose to his girlfriend, Katheleen Bourque. Ten months earlier, they had moved across the country together after knowing each other for just four days, working on a hunch about the strength of their love and commitment. 

But Lt. McDowell never returned from that training mission, he was killed when the Light Armored Vehicle he was traveling in with six other cadets hit a ditch and overturned. The cadets sustained injuries, but Lt. McDowell, who had been commanding from the gun turret, did not survive.

Read More: Tributes paid to Irish American Marine killed in "bizarre" training accident 

McDowell is the son of Michael McDowell, who was born in Belfast but spent most of his life in the US and was a key player in helping facilitate the Northern Irish peace process in the 90s.

Michael and his wife Susan Flanigan, a native of Baltimore, raised their son in the Washington, DC area. Lt. McDowell, who went by his middle name, Conor, attended public high schools before attending the prestigious The Citadel military academy for college. 

Kathleen Bourque is a native of North Carolina and last summer had just graduated from Loyola University in Baltimore with a degree in Psychology, and a special focus on mental health in the military. She had messaged Lt. McDowell via a dating app back in March, but he didn't see her message until June. 

They began texting frequently, then having phone conversations that lasted through the night, she told the Baltimore Sun, bonding about their Irish roots and passion for mental health for service members. Then in July, days before Lt. McDowell was to head west for Camp Pendelton, he decided to visit her in North Carolina, where she had moved back home after graduating.

When he arrived from Baltimore to take her out on a date, Kathleen said she knew he was the one. "I stopped and looked over the banister, and that was it...There's no explanation. Every fiber in my body was just screaming, 'That's the one. He's it!' I knew I was going to marry him in that moment," she told the Sun

They had four days of fun, traveling her hometown and going to an amusement park where he helped her overcome her long-standing fear of rollercoasters. Then, it was over pints of Guinness at Connolly's on Fifth, an Irish pub in Charlotte, that they decided they did not want to be apart.

So, much to her parents' surprise, she packed a bag and drove across the country with him to San Diego. There, they found an apartment and began building their family with two cats and a labrador puppy. 

On Monday, May 6, Lt. McDowell left for a 10-day training mission. On Tuesday, she told the Sun, he called to tell her he had been promoted to Lieutenant but that he would wait until he was home to put on his pin, wanting her to be the one to do it.  

The LAV accident that claimed his life took place three days later, on Thursday, May 9.

Since then, Kathleen has returned to Baltimore, living with Lt. McDowell's parents for the time being. At his memorial service last Friday, she said: "Conor and I chose to love each other in the hardest, most passionate, most insane way possible... because it's the only way we knew."

Lt. McDowell is to be buried in Arlington National Cemetery with full honors. 

Speaking with NBC, McDowell's father said he would not be satisfied unless there was a “rigorous investigation” into his son’s death. 

According to the Washington Post, every year since 2015 training deaths have outpaced combat deaths, and in 2017 the ratio was four to one. Camp Pendelton was the site of another training death in April, when Staff Sgt. Joshua Braica died after his tactical vehicle turned over during training. And, per the Baltimore Sun, two more service members died in training rollovers in the weeks following Lt. McDowell's death. 

Kathleen has been reading through his journals in the weeks since and shared the following passage with the paper, written after a 2018 training mission at Fort Irwin, during which there had been three vehicle rollovers: 

"It's a miracle no one was killed," Conor wrote. "...This is a reminder that at any moment through careless action even in training Marines can die."