Bower, Elizabeth (Mrs Drinkwater)
Daughter of a vicar, 'a striking girl about his own age', Drinkwater meets her in the first book, 'An Eye of the Fleet', and they are married in the period between that book and 'A King's Cutter', when he is working with Trinity House.

 
De Lancey, Charlotte
Delancey's distant cousin, daughter of James De Lancey. She is sixteen when they first meet in New York in 1776, at which time Delancey finds her unattractive. In November 1776 her home in Bloomingdale is raided by rebels, and the family moves into New York. Delancey offers to call out the leader of the rebel band, if he can be identified, a gesture which helps cement his social position.
Over the next eighteen months, Delancey and Charlotte, who grows prettier as she grows older, become attached; they correspond in secret through Charlotte's maid, Susie, who eventually shows a letter to Charlotte's mother. The couple are forbidden to see each other again, Charlotte is engaged to a Mr Bayard, and Delancey is put to sea in Falcon.
Charlotte eventually marries Mr Bayard, but Delancey is said to remember her until the day he dies. (The Guernseyman)

 
Fitton, Maria
The scolding but ultimately loving wife of Michael Fitton. In her self-reliance and from my own experience of (Merchant) Navy wives, probably one of the most convincing characters in the entire canon.

 
Harte, Molly
Wife of Captain Harte, port captain at Port Mahon, with whom Aubrey has an affair (Master & Commander), thereby antagonising Harte and jeopardising his career.

 
Hornblower, Maria
Hornblower's first wife and mother of his three children, two of whom die of smallpox in infancy. A stark plebeian contrast to Lady Barbara Wellesley, whom he meets in The Happy Return, and she meets in A Ship of the Line.

 
Villiers, Diana (Mrs Maturin)
Black-haired, beautiful, blue-eyed and pushing thirty when we first meet her; an orphan given houseroom by her aunt Mrs Williams when she comes home from India after being widowed, and meets Aubrey and Maturin who have taken up residence in Sussex after the Peace of Amiens. "Fast", unscrupulous and poor, she attracts both Aubrey and Maturin in Post Captain. Maturin falls in love with her, but is too conscious of his lack of looks and fortune to press his suit. Aubrey has an affair with her, though he has fallen for her cousin Sophie, later to be his wife. When the war resumes and he is with the fleet at Dover, she is living at Deal; he neglects his duties to be with her, endangering his career. She ends Post Captain "under the protection" of Canning, a wealthy Jewish Bristol merchant, but continues to figure in the subsequent books of the series.

 
Volterra, Gianna, Marchesa di
A friend of Ramage's during his Italian childhood, he rescues her from the invading French in the first Ramage nove (Ramage), and she lives with his family in England for some time. They appear to be in love through several books, but eventually she returns to Italy.

 
Wellesley, Lady Barbara (Lady Hornblower)
The sister of the three Wellesley brothers, one Viceroy of India and later Foreign Secretary, one the later Duke of Wellington, and one Ambassador to Spain. She and Hornblower come together in The Happy Return but Hornblower initially refuses her. By the time of A Ship of the Line she is married to Sir Percy Leighton, but eventually she marries Hornblower after Maria's and Sir Percy's deaths in Flying Colours, completing the original Hornblower trilogy.

 
Williams, Sophia (Mrs Aubrey)
Tall "with wide-set grey eyes, a broad, smooth forehead and a wonderful sweetness of expression - soft, fair hair inclining to gold; an exquisite skin" and a complete contrast to her cousin Diana, with whom she is a constant character in the Aubrey series. She is an heiress with ten thousand pounds when Aubrey and Maturin meet her in Post Captain while they are living in Sussex during the Peace of Amiens.
Aubrey falls in love with her, Sophia responds, and initially Sophia's mother looks with favour on the suit, Aubrey being rich with the prizes taken by the coincidentally named Sophie. When Aubrey loses his monery, Mrs Williams changes her attitude and stops her daughter seeing him; Aubrey then has an affair with Diana.
Sophia is however still in love with him, and egged on by Maturin conspires to have Aubrey give her and her sisters passage in Lively from Plymouth to Sussex. At the end of the voyage and of Post Captain they have come to an understanding; neither will marry anyone else.