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Tear Jerker: Gettysburg
Considering the forgone nature of the conclusion it's not very surprising. Still, it's horrifying to see what happens to these men.
ANYTHING to do with Pickett's Charge:
General Pickett's quiet horror, then screaming, "I can't see! I can't see what's happening to my boys! What's happening to my boys!?" when he realizes how badly things are going, as well as his response to General Lee's inquiry about his division — "General Lee... I have no division" — are well beyond the threshold to hold back the waterworks.
Longstreet is so certain that Pickett's Charge will fail that Longstreet is too choked up to order the assault. When Pickett asks him if he should begin the attack, the best that the heartbroken Longstreet can manage is a wordless nod.
Made worse by how eager and elated Pickett is to carry out the order, which he's asking for in the first place because Alexandernote artillery chief of Longstreet's corps which Pickett's division is part of informed him that he must "Hurry up, for God's sake, or the artillery can't help you!" The problem is, a prior scene had Alexander telling Longstreet in person that the artillery was running low on ammonote meaning that he'd have to cut down on either bombarding the Union artillery or supporting fire for the Confederate infantry and that his guns weren't having the desired effect of clearing out the Union artillery, to which Longstreet could only tell him to grab some more ammo and keep the fire on because he couldn't send in Pickett's division or the others until at least some of the Union guns had been cleared from the ridge... which means that Longstreet and Alexander both already knew that the plan was doomed.
Before this there is a moment right after the planning session where Longstreet manages to catch Pickett alone and asks him "George... can you take that ridge?" Pickett's response is a cocky smile, but Longstreet's expressionnote to say nothing of his inability to meet Pickett's eyes and the swelling music make it very clear what is about to happen. Can be seen here starting at 5:40.
When General Armistead learns he and General Hancock have both been wounded. (Though Armistead would never know it, Hancock survived his wound and continued to fight to the end of the war.) Even more because Richard Jordan, who played Armistead, passed away shortly after filming wrapped.
Armistead: I... would like... to see General Hancock. Can you tell me... where General Hancock may be found?
Thomas: I'm sorry, sir. The general's down, he's been hit.
Armistead: No! Not... both of us! Not... all of us! Please, God!
Even moreso when you learn that the production crew learned of Jordan's passing while they were in the process of editing this very scene.
There's far too many of these moments to count, but major ones include:
Armistead: (to Longstreet) Win was like a brother to me. Remember? Towards the end of the evening, things got a little rough. We both began to... well, there were a lot of tears. I went over to Hancock. I took him by the shoulder. I said, "Win, so help me, if I ever raise my hand against you, may God strike me dead."
Then there are the moments that just make you want to shed Manly Tears of joy:
The arrival of Reynolds on the first day. It's hard not to get just as choked up as Buford when you see him ride up to the Seminary.
Chamberlain's order to refuse the line. The swelling of the music and the camera tracking Chamberlain as he rushes down the line to place the men, and seeing his sheer determination to Hold the Line.
And of course the charge of the 20th Maine itself.
The reunion of the Chamberlain brothers at the end.
Although the actual fighting at Devil's Den isn't shown, an earlier scene on July 2nd has Hood protesting the order to attack the Union left flank head-on, due to the conditions being so lopsidedly advantageous for the defender; problem is, Lee already shot down Longstreet's own arguments for a flanking maneuver towards the right and the Union rear. Later on, Longstreet is shown walking into a field hospital where Hood lays ashen-faced, slow of speech and possibly delirious. After inquiring about his division's casualtiesnote he was wounded early on, so the rest of the fighting was carried out by his subordinates and requesting credit for his troops, Hood broken-heartedly sobs that Longstreet should have let him go to the right... cue Longstreet slowly, wordlessly walking out in melancholy into a similar scene of carnage outside, symbolizing just how bad it was for Hood's men. If one keeps in mind the stories of Longstreet favoring a big flanking maneuver on July 3rd, these scenes essentially are Foreshadowing Pickett's Charge.