People may remember Rob Brassington - notable for his website on Victorian era guns and the videos on his website where he describes how they worked.
He has done a video showing how the 12inch Siege Howitzer of 1916 was assembled in considerable detail with the loading and aiming sequence.
https://www.youtube.com/watch?v=vVWSn1Fpu10
The 12inch Siege Howitzer often is overlooked in favour of the more numerous 9.2inch Howitzer and the monstrous but ineffective 15inch Howitzer.
Arguably the 12inch Howitzer was more capable than its smaller and larger siblings.
Charlie