John Mills did not receive an Oscar nomination, despite receiving a BAFTA nomination and winning the Volpi Cup, for portraying Lieutenant Colonel Basil Barrow in Tunes of Glory.
In the early scenes of the film Mills effectively puts up the front of the proper leader who wants to get his regiment into shape, in a normal fashion. Mills does well to actually play into the thinness of this prospect as he does not portray a direct passion, rather he emphasizes just a man who wants things in order as they should be in a professional fashion. This earns the man little respect from most of the men, particularly not Jock who worked his way up to command after starting out as a boy in the regiment. Mills again is good in portraying the internalized exasperation of the man as he conveys the active effort of Barrow to stay on good terms with everyone, while attempting to lay down the law as a proper commander. The problems only continue as Jock's behavior only gets more out of control and the insubordination continues. Mills's performance works wonders as he reveals technically the man's fault as he does not press issues, but also a real earnestness as he shows only a man with the utmost respect for the regiment itself.
In the scene where Barrow reveals his own connection to the regiment, having been part of it the same year Jock was in prison for his usual drunken behavior, Mills reveals such a genuine passion in the man's words as he attempts to explain how important the regiment truly is. Mills is painful to watch, in a good way, in the moment because he has Barrow only reveal the truth as though he is talking to a trusted friend, yet Jock only continues to mock him when he learns Barrow was a POW in the war. Now this aspect of Barrow's past is especially well handled by Mills's performance. Mills never emphasizes in order to wholly reveal what his terrible prison time has done. Instead Mills wears it within Barrow as a man which again is a brilliant approach. Mills in doing so quietly reveals the trauma in his more intimate moments yet the wear the rest of the time seems to paint the man as though he does not quite have the needed confidence for a proper leader. Mills allows us to see the man while at the same time he presents the "coward" to Jock.
Jock forces a direct power struggle by hitting an enlisted man, an action that should lead to court martial but it is up to Barrow to initiate the charges. Again what's great about Mills's work is that he gives us everything while having Barrow only exude an indecisiveness towards the rest of the men. Mills gives us a man conflicted by his belief in the regiment and desire to hold true to the old guard, but again it only appears as weakness at a glance. Eventually Barrow decides to try to make truce with Jock, and again Mills is incredibly moving by bringing such honesty in the warmth he brings as man who only wants best for regiment. Jock claims to agree to support him but such support never materializes. This unfortunately also leads to any potential support to dry up since he did not court martial Jock when he should have. Mills is heartbreaking in the scene as he watches this betrayal, as the men mock his authority right in front of him. Mills wears the terrible anger and despair so effectively, that he makes Barrow's final actions merely seem an inevitability. It is the best performance I have seen by John Mills, as he matches Guinness's work not trying to go against him, but rather by working around him to craft a tragic portrait of soldier broken by his own men.