Generations of pupils unknowingly walked past a live World War II shell that had been the centrepiece of a display at a Devon secondary school.
The 3ft high, 111lb (50.3kg) German device had been regularly polished at St Peter's High School in Exeter.
It had been donated by an RAF Lancaster bomber crew member to the school's Combined Cadet Force in the 1960s.
But a bomb disposal team from Plymouth was called in when a military visitor realised the warhead was live.
The device, which contained 2lb (0.9kg) of explosive, was taken away to Sandy Bay firing range near Exmouth under police escort, and blown up.
The school declined to comment.
Acting Sergeant Mat Helm from Exmouth Police said: "It went off with quite a bang.
"I think the school are fortunate it didn't go off beforehand."