The princess, 44, who became a lieutenant in the organization last fall, also ate rations and attended briefings as she mingled with other ranks.
She took to the water for naval maneuvers, donned a hi-res vest to operate heavy machinery – and slipped into camouflage to fire rounds from a machine gun.
Princess Mary was one of more than 5,000 volunteers involved in the two-day exercise, designed to support the Danish Army, Navy and Air Force in either domestic or international missions.
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The big moment happened outside Bülow’s Barracks in Fredericia, 135 miles east of Copenhagen.
The princess lined up shoulder to shoulder with more than 4,500 other guards to parade in sunny conditions that have caused solders in the past to fall to the ground due to the extreme heat.
There, she came face-to-face with her mother-in-law Queen Margrethe, 76, who walked nearly a quarter of a mile to inspect the line of troops.
The Queen has had plenty of practice dealing with family members in uniform: her eldest son Crown Prince Frederik, 48, began his military career in 1986 and has subsequently achieved senior rank in Denmark’s Army, Navy and Air Force.
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Now, the question is, will we be seeing Princess Kate in fatigues anytime soon?