A retroactive example, of sorts. After discovering that Godfrey had been a conscientious objector during the First World War, Mainwaring is somewhat mean to him. He is then highly embarrassed, as it later turns out that Godfrey, despite his refusal to bear arms during the conflict, still insisted he be allowed to serve as a stretcher-bearer. And then went on to earn the Military Medal rescuing injured comrades from no-man's land.
The ease with which Fraser, Jones and Mainwaring go to what they perceive as their certain death to slow down what they think is a German invasion force to give the regular army time to mobilize in The Battle of Godfrey's Cottage is as awesome as it is touching.
Another Mainwaring moment in "Asleep in the Deep". The Platoon have to get to a sick Godfrey but the way in is blocked by rubble and the ceiling could come down at any second. They draw lots to see who will have to take the dangerous task... and Mainwaring rigs it so he "wins". He's egotistical and frequently incompetent but he's brave as hell.
Yet another in the motion picture, in which Mainwaring faces down a Luftwaffe officer while armed only with an unloaded pistol. The German's gun was unloaded too, but neither of them knew the other's gun was harmless, and the German blinked first.
After spending most of an episode being pushed around, Wilson taking out three Irish men, who managed to beat up a good portion of the squad - and coming out (mostly) unscathed!
Hell, it looked like the only thing the Irishmen did to him was bruise his knuckles with their faces!
The end of the Dad's Army movie where the platoon manage to defeat three German pilots holding a church congregation hostage while the 'regular' forces merely dither.
The flashback with Jones in the Sudan, in which he saves his cowardly teammate, fights off two bandits and then drags him to the relief column. Hands down one of his finest moments.
Wilson got another moment after Warden Hodges began harassing Mrs. Pike. Wilson goes up to him and punches him in the face, much to the approval of most people present.