The Queen met a Bletchley Park veteran as she helped mark the centenary of the Women's Royal Naval Service (WRNS) and the Women's Army Auxiliary Corps.
The visit to the Army and Navy Club was the Queen's first public event in London since her Balmoral summer break.
It comes a day after the announcement she will not lay a wreath at the Cenotaph this year as part of the annual Remembrance Sunday ceremony.
Accompanied by the Princess Royal, the Queen was given an insight into the work of the WRNS100 project, which is celebrating the formation and history of the organisation and recognising the role of women in the Royal Navy today.
The Queen, who is patron of the WRAC Association, met senior naval and army members alongside veterans who joined the Auxiliary Territorial Service (ATS) in 1941 and worked at Bletchley Park until VE Day.
Betty Webb, 94, of Birmingham, was with the ATS from 1941 until 1946.
She worked at Bletchley Park registering the messages which came in and said she felt "very privileged" after meeting the Queen.
The Queen will watch the Remembrance Sunday ceremony on November 12 in Whitehall from the balcony of the Foreign Office and the Prince of Wales will take her place in laying the floral tribute on behalf of the nation.
Mrs Webb said: "It is saddening but I think it is wise because all that standing for that length of time - it would frighten me to death. Just knowing that she will be there will be important.
"We were both in the ATS at the same time. The Queen was younger than me - she was serving as a mechanic when I was serving in Bletchley Park."
After meeting the Queen, Mrs Webb said: "It was absolutely wonderful.She was so sweet. She is such a gracious lady."
The Queen asked a small group of ATS veterans - all aged between 90 and 94 - where they served.
Joan De Vall, 92, of Leicestershire, was in the ATS from 1943 until 1946.
After speaking to the Queen, Mrs De Vall said: "She (the Queen) said I was looking very well and I said 'so are you ma'am'."
She added that being part of the ATS had made her feel "that every soldier to me is (like) my brother."
WRNS100 in 2017 is celebrating the valuable work still done by the WRNS Benevolent Trust and the Association of Wrens.
There are about 116 national and regional events planned, culminating in a service at Portsmouth Cathedral in November, during which a commemorative stone marking the formation of the WRNS and all the women of the Naval services will be dedicated.