Although the practice of subduing unit shoulder patches was officially adopted during the Vietnam war, there were some units that refused to subdue their patches because of unit pride. The 101st Airborne Division was the major one that never subdued their shoulder patches. The 101st did not subdue the patch until BDUs started to be worn.
A gravity bomb or napalm tank is moving at the speed of the plane when released, and only picks up downward velocity at 32.2 ft/sec per second. So it drops 16 ft the first sec, 48 ft the second sec, another 80 ft the 3rd. It's moving forward about 300 mph or 440 ft/sec, roughly the field of vision or six lengths of an F-4 in a second. So the F-4s dropped their loads about a second or over 400 feet before you even see them. The film has it right.
By 1969, most US Army troops, as well as other branches of service during the Vietnam War, would have been issued and using the M16A1 (with bird-cage flash suppressor), instead of the XM-16 depicted in the movie.
At base camp, when the soldiers are playing in the water, the song "I Feel Like I'm Fixin' To Die Rag" by Country Joe and the Fish is playing in the background. While the studio version had been released by May '69, the version in the movie was recorded at the Woodstock Music Festival, which took place a few months later in August '69.
When Sgt Franz is calling in an arty strike, he repeats "Rounds out" every time he heard an arty piece being shot. The correct radio comm procedure would have been the arty unit to call "Rounds over". Franz would have responded "Rounds out". 2-3 seconds before the rounds impacted, the arty unit would have radioed. "Splash over". Franz would have responded, "Splash out". This lets friendly units know rounds are coming down range and time to get down.
In the U.S. Army in Vietnam in 1969 the correct radio jargon for artillery fire missions was "Shot, over." from the artillery battery with the reply "Shot, out." from the infantry on the ground. Then came "Splash, over." and "Splash, out." Perhaps the "Rounds over" and "Rounds out." jargon was used by the U.S. Marine Corps.