Landships II

What would cause the barrel to burst at that point? Was there some sort of misfortune with the barrel or the shell it was firing? The splinter shield does not seem bent or punctured so most, if not all, of the blast and fragments must have gone forward or to the sides. I would think the crew of the gun itself would have had a nasty surprise and possible loss of limb or life if they were unlucky enough to be to the sides of the barrel when it disintegrated.