WRNS stands for the Women's Royal Naval Service — the part of Britain's navy that women served in, from the First World War until 1993, when it was closed and the women simply became members of the Royal Navy like everyone else. So it is a historical term: you meet it in war books, in family stories, in museum labels, not in news about today's navy. Two things make it worth knowing. First, almost nobody says the four letters aloud; people say "the Wrens", and a woman who served in it was "a Wren" — the initials were pronounceable as the name of the little bird, and the nickname stuck so hard that it became semi-official. Second, it belongs to a whole family of wartime British women's services with similar initials (the army's ATS, the air force's WAAF), so if you are reading about the Second World War you will meet them together. Grammatically it takes "the": she joined the WRNS, she served in the WRNS. It is a British word with no American equivalent — the US navy's women's branch was called WAVES.

英國皇家海軍婦女服務隊（1917–1993，1993 年併入正規皇家海軍）。台灣的二戰史書多半直接寫英文縮寫或譯成「皇家海軍婦女隊」，口語上英國人都叫她們 the Wrens（音同「鷦鷯」）。