In the first scene of the brothers as little boys they race from home to the railroad to see their father pull away on the train, and the last fence they have to climb over to reach the rail yard is shown first as a wooden-framed wire fence which the oldest four brothers climb over, but in the next cut to the fence, showing the youngest brother Al climbing over, the fence is missing it's wood frame and is instead an all-wire fence.
In the end of the movie, George (the oldest Sullivan brother) was in Sick Bay when the remaining four brothers go to rescue him. In reality, George and Al were the only Sullivan brothers to survive the sinking of USS Juneau. Al drowned the next day and George succumbed 4-5 days later to dementia, when he shed his uniform and swam off in search of his brothers.
The boys hear the report about Pearl Harbor being attacked while wearing their bathrobes and pajamas, suggesting it was morning. Pearl Harbor was attacked at 7:48 AM Hawaii time, which means it would have been 12:48 PM in Iowa at the time. The first radio broadcasts were made around 2:30 PM Eastern time, which would have been 1:30 PM in Iowa.
When confronting Lt. Cmdr. Robinson for the first time, both George and Frank are calling him Admiral and showing no respect for him. This would go against their training, as both had served previously in the Navy and had been recently discharged prior to Pearl Harbor (May 1941).
At the induction center, the Petty Officer the Sullivan brothers bull past has his Crow (Navy Chevrons) sewn on the mid-line of his sleeve with a crease running through the center of the chevrons. Navy uniforms have the stripes sewn forward of the crease, not on the crease.
The date on the banner at George's motorcycle race says "Sunday, July 14, 1939. July 14th, 1939 was on a Friday.
At the end of the film when the U.S.S. 'The Sullivans' is launched, the hull number 450 is visible on its bows. The hull number of the real 'The Sullivans' is DD-537.
At the ship christening, Al's wife is holding Jimmy. When the USS The Sullivans was christened in 1943, Al Sullivan's son served on board the first USS The Sullivans. His grandmother christened the first ship. The second USS The Sullivans was christened by Al's granddaughter Kelly Ann Sullivan Loughren.
Al meets Katherine Mary at a dance in 1939, where the band is playing "You'll Never Know". This song wasn't introduced until 1943, in the Fox film "Hello, Frisco, Hello," for which it won an Oscar as Best Song.
Reflection of crew member visible in mirror in parlor when mother is calling adult sons for breakfast. First scene in which sons are grown up.
When Tom Sullivan comes in from searching for George and admonishes the rest of his sons for staying up late, the mic's shadow is visible on the kitchen table.