Indeed, it’s difficult to separate the “real Olivier” and the “real Leigh” from their parts here—and the parts that had made them who they now were: he the more conservative and guilt-ridden son of a parson, she the reckless flibbertigibbet who nevertheless had a shrewd eye for power and manipulation.
-Molly Haskell, The Criterion Collection
It was 1940, Britain was in peril. Hoping to enlist the Americans in the fight against Hitler, producer/director Alexander Korda hatched the idea for this film. Cables went back and forth between London and Hollywood (where the soon-to-be Mr. and Mrs. Olivier were living temporarily, awaiting the finalization of their respective divorces). Korda had both actors under contract; he offered them bonuses, as well as the opportunity to recoup some of the money lost after their failed stage production of Romeo and Juliet. The production had to be done quickly- five weeks. Churchill would later say that it was his favorite movie.
So, your nephew sent me to you with his paintings and the bric-à-brac because he’s broke! -Emma exclaims to Sir William Hamilton
A housemaid turned wannabe fiance to one British gentleman, Emma Hart (Leigh), is suddenly shipped off to Sir William Hamilton (Alan Mowbray). He is a middle-aged widower, even-tempered, and a collector of great works of art. Sir William admires beauty. As he wishes, Emma learns languages, singing, dancing, etc. Her doting mother, Mrs. Cardogan-Lyon (Sara Allgood), is her loyal companion through it all. In time, Sir William marries Emma (making an honest woman out of her); they live in a palatial seaside home in Naples, since he is Ambassador to Italy. Though she could not be presented at court in England, the clever/vivacious Emma becomes a close confidante of the Queen of Naples.
One day, a British battleship arrives in Naples, and Cmdr. Horatio Nelson (Olivier) meets with Sir William re: docking and affairs of state. Emma bursts in on them, worried about a party she is planning. Her husband doesn’t mind, BUT Nelson insists on speaking to the ambassador in private. Emma starts to wonder if her life of is frivolous.
They told us of your victories but not of the price you paid! -Emma exclaims to Nelson (after seeing his wounds)
Five years later, Emma meets Nelson (now a lord, thanks to his MANY victories in the Napoleonic Wars) again. She is glad to see him alive, BUT also shocked by the fact that he has lost the sight in one eye and an arm. Emma wants to help, she tells Nelson, and uses her influence w/ the queen to get more troops for the war. They talk, plan, attend plays, and become close friends. Rumors start to spread…
 …when it comes to the cinema, her acting technique on screen is every bit as expert as Laurence Olivier’s. (In fact, Olivier himself admitted this when he saw her as Scarlett O’Hara.)
 Vivien Leigh and Laurence Olivier make a terrific pair and of course have great chemistry together, which really complements this true story. The actors give great performances, and I think the film really tries hard not judge the actions of Lady Hamilton and Lord Nelson which caused a tremendous scandal in their own time. Anyone who likes historical drama and wants to escape into another world for a few hours is bound to enjoy.
 Although the film was made by Hollywood, it is British to its core and fiercely patriotic. It was intended as an anti-Nazi propaganda piece… The Nazi allegory is most clearly seen in the scene when Sir William explains to his wife that the British Empire is periodically attacked by military adventurers, in Nelson’s line “We are alone but unafraid” and his speech denouncing the idea of negotiating with dictators… I imagine that it was quite a stirring film for the Britons of the day.
-Various excerpts from IMDB reviews