United first played in a semi-final at this level in their first ever season in the European Cup back in 1956/57. It was the peak of the Busby Babes era and that maiden adventure only came to an end with a 5-3 aggregate defeat against reigning champions Real Madrid. United went to the last four in the European Cup again the following season. But, having knocked out Red Star Belgrade in the quarter-finals, tragedy struck on the journey home when eight players were among those killed in the Munich air disaster. AC Milan won the delayed semi-final, although a hastily put together United side admirably won the first leg at Old Trafford.