Describing the Princess’s reaction to the lifejacket inflating, she said: “I see it a lot when we train the air crew pilots, so I knew what was going to happen and it was quite nice to watch her face.

“I think afterwards she said it was quite snug and didn’t realise how big it was going to go, and I quickly let some air out so she wouldn’t be uncomfortable.”

During her visit, the Princess spent time in the air traffic control tower and spoke over the radio with the crew of a Wildcat helicopter as it came in to land.

She heard the roar of an F-35B Lightning from RAF Marham as it “buzzed” the control tower, and was also shown around a Merlin Mk4 helicopter, which is used by the Royal Marines, and a Merlin Mk2, which hunts submarines.