Tay Ninhs weather was said to be two seasons, wet (monsoon) and dry; for us the seasons were mud and dust. They split the year fairly evenly and change was gradual during both transitions. Mud must wait for its story to be told as dust has the lead role in this tale.
The night sky is a good comparison between mud and dust seasons. On a clear night in the wet season, stars covered every space in the heavens. On moonless nights my eyes easily adjusted to the ambient light level and I could see the rice paddy country in surprising detail. The number of visible stars was multiples more than in the sky over my home of Russell, Kansas in the 1950s. During the dry season on a moonless night, Vietnams visible star count was less than 100, the light from them dimmer and they were only seen in a small circle directly overhead. Dark was much darker!
DUST was the reason. Tay Ninh air was burdened with dust from the Vietnamese living and working and our military operations. Artillery fire produces concussions that lift very fine-grained ground dust into the air and creates a dust dome over a FSB. Only wind or rain would chase the dust away and rain was on vacation. Helicopter take-offs and landings were dust cannons as well. Breathing was not healthy.
The dust was so fine-grained it could infiltrate supposedly sealed items such as a water resistant wristwatch. Moving parts on machines were in danger of being ground away as the dust inserted itself. My tan from being shirtless washed off in baths during my first week home; my skin had been protected from the Vietnam sun by a dirt shirt that would not scrub off with a brush. Petroleum lubricants were dust magnets; we spread Pena-Prime on the dust floor of the FSB to glue it down. I have no idea what the intended solution was but we created a paper thin crust on the soil, using buckets to spread it evenly. Walking on that crust built a growing pad of oil/dust on the soles of our boots. Dust won the war. It covered everything; top, bottom and in-between.
Convoys on the red clay laterite roads could be like driving in a sand storm and taste very much like one. On a calm day, the rear vehicles in the convoy tended to lag behind just to see the road. Tanks and APCs threw-up large particles along with the smaller dust; being behind one at high speed was a three-course meal.