A British officer's servant is a batman.
Lady Mary mention a 'no names no-pack drill'. The 'No names, no pack-drill' is used to indicate that the names of those who have committed a misdemeanor will not be mentioned in order to spare them punishment. Pack-drill was a punishment given to soldiers in the British Army, requiring them to undertake drill (exercise) in full uniform and carrying a heavy pack and dates to the middle of the 19th century.
Branson mentions Alexander Karensky, the Socialist leader of Russia who overthrew the Czar in 1917. However, his rule was short-lived as the same year his government was in turn overthrown by the Bolsheviks led by Vladimir Lenin.
Novels by G.A. Henty and Frederick Marryat are mentioned as reading material for convalescents at Downton. Hemty was a prolific 19th Century author of patriotic historical literature including "With Wolfe in Canada: The Winning of a Continentand" while Marryat wrote sea stories and children's literature including his semi-autobiographical novel, "Mr. Midshipmam Easy."
Thomas Campbell, who plays Captain Smiley, was the boyfriend of Jessica Brown Findlay, who plays Lady Sybil Crawley.