The Queen was granted a historic naval title ahead of her attendance at a maritime ceremony in Devon.
Camilla was appointed Vice Admiral of the United Kingdom as she visited HMS Astute in HMNB Devonport – making her the first royal in the honorary role, which dates back to the mid-16th century.
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HMS Astute, the first of her class, is the lead submarine in the Royal Navy's fleet of Ship Submerged Nuclear (SSN) or ‘Attack’ Submarines.
The ceremony marked the end of the submarine's first commission, which is the longest commission of any Royal Navy submarine in history, at over 15 years.
Her Majesty's outing comes ahead of her 78th birthday on Thursday.
"During the course of my role as your Lady Sponsor, I have had quite the education into the life of a submariner," the Queen said. "With this being the UK's first submarine to embrace the digital world, perhaps these experiences of the unknown were shared across the Ship’s Company. Indeed, her warfare trials on the Eastern Seaboard of the US were so successful, proving virtually impossible to detect, that the US Navy had to update their own exercises to match her. As for the crew, I suspect that the novelty of having one's own bunk was enough to make her 'first of class, and second to none'."
Earlier in the day, the Queen spoke of how uplifting children's hospices can be during a visit to a charity in the South West. Camilla listened to performances and spoke with care users, families and staff during a visit to Little Bridge House in Fremington, Devon, on Wednesday.
Her speech followed a game of air hockey with Daisy Clark, 15, a bereaved sibling. The Queen immediately won a point from her opponent and played a second short rally, which ended in a draw.
Addressing staff, she said: "These children's hospices are such wonderful places.
"I don't think we realise quite how lucky we are to have them. I think it would be wonderful if we could have a few more.
"Everyone who works in them and makes them such happy places deserve a huge, huge thank you."
She said on her first visit to a children's hospice she thought they would be sad places, "but they are completely uplifting".
The unit – part of Children's Hospice South West – is celebrating its 30th anniversary of providing care for babies, children and young people with life-limiting conditions, and also helps support their families.
During her engagement, the Queen unveiled a commemorative photograph of the charity's co-founder, Eddie Farwell, who died earlier this year.
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