It is said that there is nowhere in our known universe that there is liquid water on or near the surface but Saturn's moon Enceladus has liquid water just beneath the surface and so does Jupiter's moon Europa.
Just before they are first attacked, the Lt. states that the police station is "one click northwest". But when they leave the pool, the subtitle states that they are 1.3 miles from the station - at least twice the distance.
When the Gunnery Sgt. tricks the alien drone into following the radio signal to the gas station pumps, he runs about 10-15 yards from the pumps and then throws a grenade igniting them. The resulting explosion was large enough to reach him at the position where he was seeking , but it had no effect upon him or on the car he was hiding behind.
Towards the end of the movie in the FOB, when SSGT Nantz confronts Cpl. Lockett about his brother, Cpl. Lockett has some powder on his face during some of the close-ups but in other close-ups the powder is gone then reappears in the same scene.
When they exit the bus and the soldiers are repelling off the raised freeway they get fired upon and fall. The one not attached to the rope falls with his head towards the car on which the guy on the rope falls onto the bonnet. The next shot shows the first guy is laid the opposite way round, with a previously non existent car on its side behind him.
At the mission briefing, pictures taken by the Hubble telescope of the "meteors" falling to Earth are shown to the marines. Hubble is a deep space telescope, virtually useless for taking pictures of anything in Earth's atmosphere.
After staff sergeant and then the rest of the marines fast rope down the helicopter lifts out with the ropes dangling; this is never done. The ropes are always just dropped; they are considered expendable material.
When the command and control center is destroyed, the Copperhead rounds are shown with an exhaust trail. Copperhead rounds are not self propelled as they use aerodynamic surfaces to glide to the target and do not have an exhaust trail.
When some Marines are in a flower shop in their camouflage Utility Uniform. It did not appear to be a shop that was on their base. US Marines are not allowed to wear this uniform off of their military installation except to travel to and from their duty station.
When 2nd Lt. Martinez gives himself up to save the others and blows him and the alien force to bits with the C4 on the bus, the scene after the explosion shows the middle of the bus blown out with the front of the bus still intact. The amount of C4 in the bag and surrounding the bus would blow out the entire bridge from around the bus, not just the side of the bus.
The scientist interviewed on TV said that the aliens were interested in the "composition" of Earth's oceans, specifically saying Earth is the only known place in the universe with liquid water. However, he should have said "state," which means solid, liquid or gas. Water's "composition" would refer to its salinity and other mineral content.
The CH-46 helicopters that take the Marines from Camp Pendleton to Santa Monica are marked "HMM-774". Marine Medium Helicopter Squadron 774 (HMM-774) is a United States Marine Corps medium helicopter squadron consisting of CH-46E Sea Knight transport helicopters. The squadron, known as the "Wild Goose", is a United States Marine Corps Reserve unit based at Naval Station Norfolk (Chambers Field), Virginia.
A Copperhead is an artillery shell, not a missile as depicted in the film. It's best use would be in "Ballistic" mode where it is fired with high cloud ceilings and good visibility. In that mode it can be fired from up to 10 miles away and multiple shots can be taken.
For the mission shown however, a Hellfire (a guided missile fired from helicopters, ground-based platforms and drones) would have been a better choice as it can be fitted with a larger warhead than a Copperhead and its "fire and forget" capabilities make it far more useful. Marine leadership would know this and would have made the correct choice for the job.
When Nantz quotes the serial numbers of the fallen soldiers, he says them XXX-XXX-XXX. Since late 1971, the US military uses Social Security Numbers as ID numbers with the pattern XXX-XX-XXXX. It is common to say those numbers in that pattern.
At the beginning of the movie, after Nantz has had his morning workout and run on the beach, he drives up to the base guard and shows his military ID. The guard, a sergeant, starts to salute, but then stops himself. His arm only goes half way up. Sometimes real off duty, military personnel are used in movies, and perhaps this guard forgot Nantz's pretend rank, and did not know if he should salute or not. The guard would only need to salute a higher ranking officer after checking the ID, not another sergeant.
It was noted that a flight of A-10 "warthogs" were on the flight line at Camp Pendleton. The A-10 is a close support ground attack aircraft flown by the USAF in support of ground operations conducted by the Army and the Marines. They often conduct joint training so seeing Air Force craft at a Marine base is not uncommon.
In the early scenes set in Camp Pendleton, several A-10's are shown on the flight line. A-10's are flown exclusively by the U.S. Air Force, not the Marines. MCAS Camp Pendleton houses only helicopter squadrons, and fixed wing close air support aircraft such as F/A-18's and AV-8B Harriers would be launched from other nearby Marine bases such as Miramar.
The first utility vehicle SSGT Nantz fired the .50 cal from showed a close up of a spent cartridge which fell from the gun and it showed the crimp marks of a blank and not the perfect round shape of a spent .50 cal ball round.
When CPL Imlay fires the M-203 Grenade Launcher rounds down the hallway they leave a smoke trail. This is incorrect as the M-203 rounds are like large bullets and only leave a puff of smoke when fired. They are not rockets and therefore would not leave a smoke trail.
Just prior to boarding the helicopter after the alien command center is destroyed Staff Sgt Nantzs face is covered in sweat and dirt. While on the helicopter Nantzs face is now covered in sweat, dirt and blood. When the helicopter lands at the temporary FOB the blood is gone from his face but the dirt and sweat are still there.