R. Lee Ermey did not receive an Oscar nomination, despite being nominated for a Golden Globe, for portraying Gunnery Sergeant Hartman.
Although Matthew Modine as Private Joker is technically the lead of the film as a whole R. Lee Ermey is the star of its first third as the men go through boot camp. Ermey owns the picture and for most of the first third it is a constant stream of his voice in the role of the drill Sergeant who intends to shape every man his way. R. Lee Ermey actually helped Lou Gossett Jr. prepare for his Oscar winning role in An Officer and A Gentleman as a drill Sergeant. Ermey though doesn't repeat Gossett's performance, Goessett's character had a heart, Ermey plays Sergeant Hartman as the penultimate soulless drill Sergeant who will make killing machines at any cost.
Ermey's performance is a non stop charge of intensity as he rips out every insult known to man to demean and break down each man to meet his firm requirements. Ermey doesn't hold back and his performance has a visceral sting like few performances ever have. Ermey string the film along through his, mostly ad-libbed, insults he lobs toward each recruit. Ermey does not even seem to blink in his unending intensity that is perpetual in every scene that he is in. Each of Ermey's results cut right down to each matter and the way each man falls directly in line is not even a slight question because Ermey absolutely controls all in every single scene he is in, besides his final scene of course.
This performance would see one that is one note in that Hartman really does not change nor should he, but Ermey brings so much in the yelling of the drill Sergeant. He always brings that violent threat and a forced dehumanization in his almost sometimes demonic eyes. In that though Ermey even manages a very odd yet extremely effective pitch black comedy in his performance too. Ermey never does wink even slightly in his performance and his extreme nature of his character is always kept intact. Within the unquestionable drive of his performance Ermey technically does have a satirical take by being the drill Sergeant that would cause most drill Sergeants to cower in fear.
One of Ermey's best moments is when he gives a lecture to his men about the Kennedy assassination as well as well as a sniper massacre. He talks about both and Ermey has Hartman speak of them with the utmost pride as he basically praises both events simply because the men who did the killing were both trained by the marines. Ermey's delivery of it is flawless because he allows the absurdity to be there without paying any direct attention to it himself. He keeps an absolute conviction in his performance and even though the statement is completely insane Ermey is great because obviously it is perfectly sensible to his deranged idea of pride.
Leonard's ill treatment never stops as Hartman's ridicule always continues and eventually he is hazed by the other men when Hartman decides that the other men will have to suffer for every mistake Leonard makes. This results in a change in him that is rather extreme and sudden. This is not D'Onofrio's fault as he does have slight indications that this could happen beforehand, but once he changes there is no going back. D'Onofrio becomes almost entirely silent for most of his remaining scenes as Pyle is left by everyone and internalizes everything into himself. D'Onofrio is excellent showing the closed off Pyle and the insanity clearly building within him as he goes by himself to complete the task of becoming a killing machine.
This leads to the final scene where Ermey's and D'Onofrio's performances converge. D'Onofrio is amazing in the scene showing a full changed Pyle as he finally bursts out into his emotions in a truly frightening scene. D'Onofrio is chilling as he shows the formerly soft Pyle a man driven by insanity as Pyle loads and prepares his gun with actual ammunition. D'Onofrio explosion is only made more startling by the way he build in the proceeding scenes in which Pyle was clearly repressing something as he went about his duties to finally pass the trials of the marines by being the monster Hartman always wanted him to be.
Ermey comes in this scene and is also great as he dials back on the intensity of Hartman for just a moment when he notices what Pyle is planning. It is a very subtle moment as Hartman perhaps sees what he has created before he tries one more time to return to his intimidation that results very poorly for both Hartman and Pyle. It is a fantastic scene as Ermey and D'Onofrio basically play Frankenstein and his monster with Hartman having to face what he created. Both actors are brilliant in their uncompromising performances that go all the way with their characters right to their very bitter end. They both give performances that are madness incarnate, one controlled one not, and both succeed in creating the unforgettable opening act of this film.