Factual error: When Mike is leaving to join the Marines he is in full uniform. Uniforms are not issued to new recruits until after they are processed in. They arrive at Camp Pendleton in civvies.
Factual error: When Chitty Chitty Bang Bang arrives at the Potts' house, Grandpa Potts is sitting in a deckchair reading a very modern colour edition of National Geographic magazine.
Factual error: After finding the soldiers slaughtered at the Khyber Pass, Sergeant Major Mcnutt and Private Widdle try to see off the Burpers with a "Maxim". The Maxims in use at this time look nothing like the gun they use, which appears to be loosely based on a Gatling gun. Additionally, it's mounted on a MkIV tripod, not introduced to the British Army until 1906, 11 years after the film is set.
Factual error: First time I ever saw a 600 mile NASCAR race where nobody had to make a tire change.
Factual error: The film tells the stories of five male/female couples. They have conflicting aims in their relationships. For example, one wants to become a parent while the other does not want children. Thus they all obtain supplies of contraceptive pills (in bottles) and re-label them as aspirins or vitamin tablets (or vice versa) depending on whether they want pregnancy or not. The bottles get mixed up, causing panic and anxiety for all involved. All the interlocked stories are based on a complete error. Contraceptive pills are not stored in bottles. Contraceptive pills are packaged in 'blister packs'. This basic fact makes a nonsense of the entire film.
Factual error: During the opening credits, Jack Lemmon walks past two "sailors" in dress whites. If they were actual sailors, they would have rate insignia on the left sleeve, service ribbons on the left breast, and a rocker patch on the right shoulder seam.