"Actually '78 was a really exciting time for U2. We had just discovered F sharp minor. So we had the fourth chord and we'd only had three up to then."
A local violinist, Steve Wickham, approached The Edge one morning at a bus stop and asked if U2 had any need for a violin on their next album (the War album). In the studio for only half a day, Wickham's electric violin became the final instrumental contribution to Sunday Bloody Sunday.