Moaning Minnie
/ˌməʊnɪŋ ˈmɪni/Chiefly British
noun
1 Informal. A siren or klaxon, especially (now historical ) an air-raid siren.
2 Military slang. A kind of mortar or rocket launcher used by German forces in the Second World War (1939–45); especially = nebelwerfer.
3 Informal. A moaner, a complainer; a pessimist.
Origin
1940s. From moaning + Minnie, female forename, in sense 2 punningly after Minnie.