Visible crew/equipment: When the Muslim armies approach Brendan Gleason's castle there is a side shot of the Muslims army coming to a halt. You can see the marker stake with yellow tape at the top (used during production as a mark). (01:10:10)
Continuity mistake: When Cortez gets out a photo of his wife pregnant, the photo changes between shots. She is facing a different direction in the next shot. His USMC tattoo, however, stays the same direction throughout the scene. (00:26:55)
Factual error: A very common error in First World War films. British soldiers were not permitted to shave their upper lips until 1916 - in 1914 almost all (unless physically unable to grow them) would have had moustaches.
Other mistake: The exact same background shot of a Ventura bomber followed by two single-engine planes flying left to right is used three times during the film, twice at the beginning as they are planning the mission on the beach and then once at the end when the raid is over.
Continuity mistake: When Valiant flies down the gun barrel, he takes off his backpack and helmet, and he lays them down in the barrel before squeezing through the back of the gun. When he comes back out through the gun with the other birds, the backpack and helmet are not there.
Continuity mistake: When Mother and Mameha are waiting for the bid on Sayuri's mizuage, Mother's cigarette is short at one point, but becomes longer in the next shot.
Plot hole: The movie takes place before and around 1938 and, supposedly ends in that year, following the entrance in Shanghai of the Japanese, with the exodus by many Chinese and foreign residents. Ralph Fiennes' character, as an American ex-diplomat and businessman, would have resided, have bank accounts, his car, etcetera, in the foreign concessions. The Japanese did not occupy the concessions until after Pearl Harbor, so there was no need for him to flee the city, as a refugee without a passport and with little or no money, sailing towards Macao in a fragile Chinese junk. He could just have driven or walked a few blocks to any of the "Western" concessions, from where he could have married Natasha Richardson's character, obtained U.S. passports (White Russians had none, as the rest of her family in the movie until assisted by an official in the French Consulate) for her and her daughter, purchased a ticket in a safer vessel, sold his assets (regardless of the damage to his club, he still had a house, furniture, a car, presumably bank accounts, etc.).
Revealing mistake: As Uchida makes his last-stand the ships tilts heavily to the right, however none of the empty shells on the deck move, showing that it's only the camera being angled.