Factual error: This movie takes place in 1957, clear from the Sputnik reference, but at the dance they play "It's All in the Game" which didn't come out until 1959.
Factual error: The British Major at the end has his rank crowns sewn to the collar of his shirt. The British Army didn't/doesn't do that. They should be on his shoulder epaulettes.
Factual error: Near the start, the letter received from Brazil has a stamp with Brazil written with a Z, but stamps spell it Brasil, with an S. (00:08:35)
Factual error: Hornblower's plan is to sail Le Reve south from Gibraltar to give him ample sea room before he heads for England. Generally, the prevailing wind through the Straits is westerly, unless there is a Levanter, yet Le Reve is shown on a port tack when it should be on a broad reach. The fog that comes up would not exist in a gale-force Levanter.