Molly Bloom's father, a man named "Tweedy," was an officer in the Royal Dublin Fusiliers stationed in "Gibraltar" during her infancy and youth. In Ithaca he is called "Major Brian Cooper Tweedy." According to Ellmann, Joyce based Tweedy on a Dubliner who called himself Major Powell but who in fact served only as a sergeant-major, an important non-commissioned or warrant officer. This ambiguity attaches to Tweedy in the novel.
Ellmann writes of Sergeant Major Powell, "He had served many years in the army, took part in the Crimean War and was in the Aldershot Rifles in Australia. On retiring from the service he commuted his pension and bought a farm in Cork. He drank this up, came to Dublin and married a woman with property. She bore him four daughters and a son, then tired of his bullying ways and lived separately from him. Joyce has greatly softened Powell's character" (46n).
In Calypso Bloom remembers his father-in-law in a generally admiring way as a self-made man who was smart with money: "Hard as nails at a bargain, old Tweedy. Yes, sir. At Plevna that was. I rose from the ranks, sir, and I'm proud of it." Gifford notes that Tweedy could not have been at Plevna, a battle fought in Bulgaria in 1877 during the Russo-Turkish War, but apparently read about it avidly in a book that now sits on Bloom's bookshelves, Sir Henry Montague Hozier's History of the Russo-Turkish War. In Ithaca Bloom has trouble recalling the name of this "decisive battle" so "frequently remembered by a decisive officer," even though he has remembered it readily in Calypso. He resolves to use his "mnemotechnic" to recover the name, as he has done once before. His memory of Tweedy as a "decisive" man coheres with his admiration of his father-in-law's money skills.
It would have been highly unusual in the 19th century for an enlisted man to rise through the ranks to become a commissioned officer: gentlemen and noblemen typically began at the rank of lieutenant, while commoners seldom rose above the rank of sergeant. It seems quite likely that Tweedy, like Powell, was never a commissioned officer. In Penelope Molly remembers how she read a love letter from Lieutenant Mulvey "while father was up at the drill instructing." This implies that Tweedy was a drill sergeant, not a major.
Sergeant-majors are usually warrant officers, distinct from higher-ranking commissioned officers on the one hand and lower-ranking enlisted men and non-commissioned officers on the other. They occupy an important and honorific position in the British and many other armies. The fine distinction between warrant officers and commissioned officers, and the confusing use of the term "major" to name officers separated by great distances in the hierarchy (sergeant-major, major, major general), gives a retired officer like Powell the ability to imply a more exalted military status than he in fact can claim, by exploiting civilian incomprehension. Nevertheless, any enlisted man who "rose from the ranks" to achieve the exalted rank of sergeant-major might have been justly proud of his accomplishment.
A little later in Calypso, as Bloom imagines himself wandering through the exotic streets of a Middle Eastern city, he places a version of his father-in-law in the scene: "come to a city gate, sentry there, old ranker too, old Tweedy's big moustaches, leaning on a long kind of a spear." This old man too has risen through the ranks. Apparently the places that Tweedy has seen in his days of army service give him an exotic air in Bloom's mind.