If you are talking about cheering during the Anthem for 'Hawks games...it started for the 'Hawks not the troops.
There are basically two different versions of why the cheering during the National Anthem started, atleast what I have been told over the years. Pretty sure this is what you are alluding too but I'll expand since it seems few people know the reasons.
1. 1985 playoffs - The Oilers' fans boo and are disrespectful in general to the National Anthem during a home game in Edmonton. Instead of booing Canada's, the Blackhawks fans instead cheer for our National Anthem.
2. 1985 playoffs - Blackhawks fans are so excited for the game that they cheer throughout the National Anthem and it sticks.
The cheering sort of came to light during the 1991 All Star game during the Persian Gulf War. There are plenty of videos around the web from that day.