Factual error: The climax of the first episode, The Battle of The Tenaru River, is not historically accurate. Leckie did not run about shoring holes in the Marine defensive line. The real heroes of the engagement known variously as The Battle of Alligator Creek (a misnomer - no alligators in the South Pacific), Battle of the Tenaru River (mismarked on Marine maps, properly known as The Battle of The Ilu a tidal lagoon) were Marines Leroy Diamond, Al Schimd and John Rivers. These men accounted for over 200 Japanese KIA. All three paid dearly. Rivers was killed, Diamond sustained over 8 bullet wounds and Schmid was blinded. For their gallantry in action the three were awarded the Nation's second highest honor the Navy Cross. An accurate depiction of this battle was in the movie "Pride of the Marines."
Continuity mistake: In the scene where John Basilone goes looking for his friend Manny. Basilone has 3rd degree burns on his left forearm and left hand but in the shot he is walking through the jungle holding a pistol tightly in his left hand and his canteen is on his right side as he walks past a group of trees. The next shot he is continuing walking through the jungle but the gun is in his right hand (which isn't burned) and his canteen has also switched sides as he walks past the same group of trees.
Continuity mistake: The Pacific Complete Series, Episode 6: A soldier kneels down next to a covered dead soldier's body to check his bottle of water. When uncovering the body, the face of the dead soldier faces to the right. In the next shot, the face is to the left, and then before being covered again the face goes back to its original position of facing to the right. 10m:30s to 11m:10s.
Factual error: Robert Leckie returns to Bergen County, N.J. in the mid '40s. While talking to his dad he says of that afternoon "Bergen Catholic plays Don Bosco Prep." Bergen Catholic wasn't established until 1955, and while Don Bosco did exist in the 1940s, it didn't have a football program until the late 1950s.
Continuity mistake: In Episode 4, after a Japanese counter attack, Leckie is talking to two other soldiers. In the first shot you see him walk to where the .30 cal machine gun position is located. The machine gun is uncovered, then after the camera switches to the dead Japanese and back to machine gun, it's covered by a water proof tarp. Then it shows Leckie again as he's lighting a cigarette with just the tip of the .30 cal machine gun muzzle uncovered.
Factual error: John Basilone was actually a Sergeant when he won the Medal of Honor at Guadalcanal, but is shown wearing the insignia of the higher rank of Platoon Sergeant. However, when his medal citation is read out it does give his correct rank (although senior sergeants in the US forces are commonly addressed simply as "sergeant", official citations give their full rank).