This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / We Were Soldiers
Literally invoked by the effects of napalm. Especially on poor Jimmy Nakayama... He's so badly burned by the napalm that when Galloway goes to grab his legs to carry him to safety, his skin peels off his legs. That's not creative liberty on Hollywood's part, that actually happened.
The onscreen deaths of the soldiers. Crosses over with Tear Jerker when the wives are notified of the deaths of their husbands.
One soldier is hit with White Phosphorous—or Willy Pete—in the face from a Vietnamese grenade. White Phosphorus, once ignited, burns at well above 2500 degrees Fahrenheit, and will continue burning while immersed in water, as it simply pulls oxygen from the water to maintain combustion. A fellow soldier has to carve out the burning fragments out of his face with a knife.
While training stateside before their deployment, Moore's radio operator is able to tune in on broadcasts from US forces in a firefight on the far side of the world. Moore's men are able to do no more than passively listen to the urgent radio message as the sounds of a pitched gunbattle can be heard, while being helpless to do anything to aid the troops in the battle.