In a statement posted on Twitter, the duchess thanked the armed forces and their families for the “sacrifice” they make to keep the UK safe.
“Today on #ArmedForcesDay, William and I would like to pay tribute to the brave men and women, past & present, serving in all of our armed forces, at sea, on land & in the air, here in the UK and around the world,” she said.
“Thank you for all you and your families sacrifice to keep us safe.”
The duchess also shared some photos from her visit to Pirbright Training Academy and Abingdon airfield in November last year.
“Last year, I was honoured to spend time with the @BritishArmy to see how they train serving personnel and new recruits,” she said.
“It was wonderful to see first-hand the many important and varied roles the military play day in, day out to protect us all.”
She added that she looked forward to discovering more about the Royal Air Force and Royal Navy “in due course”.
During her visit the duchess saw first-hand how new recruits and serving personnel are trained.
She even took part in some of the training exercises and spent time speaking to the soldiers about their experiences in the British Army.
The photos echo those taken of her mother-in-law Princess Diana, sitting in the driver’s seat of a tank in 1988.
Similarly, a young Prince Harry was also photographed wearing a slightly-too-large helmet while on a visit to the barracks of the light dragoons in 1993.