### Clue: Inappropriately merry band came to swamp English solemn occasion (11,3)
### Answer: REMEMBRANCE DAY 
 ### Explanation: Definition: solemn occasion
 **Anagram of**(Inappropriately) MERRY BAND CAME **containing**(came to swamp) E(abbrev. for "English").
Defn: … to commemorate those killed in the World Wars.