He quickly found his feet, leading convoys of armoured vehicles through the streets of Baghdad and into the desert.
One morning, his crew was targeted in a roadside bomb attack and Callender became Australia's first serious casualty in the war.
After recovering from his injuries, he returned to Iraq in 2006 as second-in-command of the Australian Army's security detachment in Baghdad.
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READ NOWHis unit had to contend with missile attacks, suicide bombers and the death by misadventure of one of their own, Private Jake Kovco.
Callender volunteered again in 2009 to lead a weapons intelligence team in Afghanistan.
From there he was flown to blast zones in the aftermath of attacks and worked to identify the insurgent bomb-makers responsible.
After the Blast: An Australian Officer in Iraq and Afghanistan is his story.
Callender will be at Joondalup Library, 6.30pm, July 28.
Cost is $4. To book, call 9400 4751 or go to www.joondalup.wa.gov.au.