Britannian Superheavy Railway Gun

The Britannian Superheavy Railway Gun is an immense artillery platform used by Euro Britannia to shell Europian positions in the Eastern Front.

It is largely dependent on tracks and its large size and limited movement makes it vulnerable from enemy counterattack. As such, several Knightmare Frames are used to guard these vehicles from enemy attack. Nevertheless, despite these vulnerabilities, its immense calibre of its gun mixed with its incredible range of 500km and firepower, makes these Railway Guns a formidable weapon to be used against the United Republic of Europia.

Code Geass: Akito The Exiled
In the OVA, a few of these were stationed in the Easter Front to shell the positions of the Alexanders, half of which was automated and operated by Leila Malcal. Despite the immense blast destroying a few of them, their fast speed and agility means that the majority of the Alexander's survived the barrage.

Trivia

 * It carries the largest gun by calibre in the Holy Britannian Empire, only being beaten by the likes of Longdan and Da Longdan.
 * It's function and sheer size is reminiscent of the Schwerer Gustav.