Kaiser's Goliath Gun

Egad! A 42cm cannon that fires 2800lb shells!
Sounds like a grand target for the Royal Aeronautical Service to take out!

http://www.greatwardifferent.com/Great_War/Goliath_Gun/Goliath_Gun_01.htm

http://www.landships.freeservers.com/420mm_morser_m17.htm