This is the last episode with Roger Leclerc (played by Jack Haig). The departure of Roger Leclerc isn't explained because Haig was set to continue in the next season. Unfortunately, Haig died on 4th July 1989, before the next season started.
When Colonel Von Strohm orders Lieutenant Gruber to take off his uniform, Helga & Captain Bertorelli perform the tune of, The Stripper, composed by David Rose. 'Allo 'Allo! is set during WWII, but the tune wasn't written until 1958, 13 years after the war had finished, meaning the joke is not in keeping with the timeline of when the show is set.