Kate was photographed gingerly getting into a Super Hornet at an Australian air force base near Brisbane Saturday.
Following husband William, who'd been in the front of the cockpit, Kate was unexpectedly ushered to get in as well.
William, 31, had offered her the seat behind, saying, "Do you fancy jumping in the back?" She asked, however, to sit up front, and her husband made way, moving to the back seat as Kate, 32, climbed in.
The duchess later flashed a big smile as she sat at the controls.
Stephen Chappell, commanding officer of Number 1 Squadron, whose pilots fly the Super Hornet, said Kate was fascinated by the "dials and gadgets" on the fighter aircraft.
Tim Rooke / REX USA
The couple were at RAAF Amberley in Queenstown, Australia, to meet veterans and their families in the officers' mess.
Kate – who wore a summery white L.K. Bennett dress with royal blue flowers, which she paired with navy-blue suede heels while clutching a royal-blue bag by Australian designer Oroton – had arrived from Sydney with William, whose first role was to inspect Number 1 Squadron, which was embedded in the RAF during World War I.
They also carried out a royal tradition of planting a tree at the base's memorial garden, as a tribute to the fallen.
Kate was presented with a bouquet of flowers by Ashleigh Kearnan, 9, whose father, Lieutenant Charles Kearnan, is a ground-defense officer who had served three tours of Afghanistan. Later, 3-year-old twin brothers Ellijah and Tobee Dyer provided a moment of humor when they presented a boomerang to the couple.
As William took it, the boys shook their heads and told him, "It's not for you – it's for the princess to give to George.