Python 2, 117 bytes
s="ABCDEFGHIJKLMNOPQRSTUVWXYZ"*2
for i in range(len(s)):print s[0:i]+s[i::-1]if len(s)/2>i else s[0:-i-1]+s[-i-3::-1]
s="ABCDEFGHIJKLMNOPQRSTUVWXYZ"*2
for i in range(len(s)):print s[0:i]+s[i::-1]if len(s)/2>i else s[0:-i-1]+s[-i-3::-1]