In this play, one of the main themes is heroism, and its opposite form, cowardice. How does Sherriff explore this in Act 1?

In Journey’s End, a play about English troops on the French front during World War I, the first act is primarily exposition. Among other characters, the author introduces and establishes a pre-existing relationship between Captain Stanhope and Lieutenant Raleigh.
Through conversations between other characters, notably Captain Hardy and Lieutenant Osborne, it is established that Captain Stanhope has developed a drinking problem and is having serious difficulty coping with the war in which he has been serving for three years. Osborne, who is second in command, steadfastly maintains his faith in the commander. Raleigh and Stanhope not only knew each other at school, but Raleigh is now engaged to Stanhope’s sister. Raleigh is shown to have a case of hero worship for Stanhope, who is just a few years older.
The play’s plot overall concerns an upcoming German attack and the English troops’ preparations for it. In Act I, we learn about Stanhope’s conflicting attitudes. He has high standards for his men and criticizes Second Lieutenant Hibbert for suspected malingering, as his ailment is neuralgia. In contrast, he seems more concerned with his reputation than his actual performance, as he worries that Raleigh, in his letters to his sister, will inform her about his excessive drinking.
https://archive.org/stream/in.ernet.dli.2015.209119/2015.209119.Journeys-End_djvu.txt