Last week, Australia lost a friend. Shawn Brimley, who passed away following a short but brave battle with cancer, worked tirelessly to modernise the US defence establishment – a central pillar for regional stability and, by extension, Australian national security.

Shawn was a naturalised US citizen – he was Canadian by birth. Perhaps because he was an immigrant, “he really believed in the power of American leadership and America’s unique role in the world” said Derek Chollet, his former boss in the Obama White House.

In 2007, Shawn was a founding member of the Center for a New American Security (CNAS) in Washington DC. Joining others from the venerable Center for Strategic and International Studies, he, along with his colleagues, sought to develop defence and foreign policy that was forward thinking and, as importantly, practical.

Shawn had his first chance to apply his ideas when he joined the Obama administration in 2009. Starting in the Pentagon, he wrote a good portion of the 2010 Quadrilateral Defense Review – a congressionally-mandated study on US Defense objectives and threats to national security. Later joining the White House National Security Council, Shawn was a major architect of the 2011 announcement to rotate US marines through Darwin. On leaving the administration in 2012, he could easily have joined the defence industry or a major consultancy. Instead, he returned to and remained at CNAS.

To the end, Shawn was driven to adapt the US military to rapid changes in both technology and geopolitics. Work in this space included the widely-read Foreign Policy article “Ctrl+Alt+Delete”. But a more lasting legacy will be his role in the “third-offset strategy” – a series of strategies announced in 2014 designed to sustain US military-technological advantage (I recommend reading a well-researched piece on this by Brendan Thomas-Noone).

Personally, Shawn was and remains influential. When I was an intern at CNAS, I was parked right outside his office. Everyday, no matter how tough his work or long his hours, he would always come to check on me. We would talk about my career, family, books and movies. Ongoing were his jabs at me for being Australian – I would fire back by saying he was really a Canadian.

It was these interactions, and others at CNAS, that showed me what it meant to be a leader and public servant: presence, dedication, self-awareness, grit, openness to new ideas, a wicked sense of humour and a genuine investment in one's colleagues and mentees. Since leaving, I’ve tried to live these values at the USSC (when I supervised interns myself) and now in the Australian Public Service.

The loss of Shawn Brimley is a loss for Australia. The eulogies and outpouring on social media from the US national security community is a testament to his tragically brief but important impact. But Shawn was also a thoroughly decent man. The world is a lesser place without him.

He is survived by his wife Marjorie and his three children; Claire, age 8; Austin, age 6; and Tommy, age 3.