TIL the longest ever tank-to-tank killshot was scored by a British tank crew during the Gulf War (1990). It was from over 2.9 miles (about 4.7 km).

https://en.wikipedia.org/wiki/Gulf_War#United_Kingdom

https://www.reddit.com/r/todayilearned/comments/152zpri/til_the_longest_ever_tanktotank_killshot_was/