Well that's actually a Howitzer, which was designed to fire shells from an angle of 45 degrees up to 90 degrees. This was ideal for trench warfare, but more usually for engaging hidden targets (such as to the rear of hills etc).
Guns of that calibre
would have been mounted at Braefoot, though designed for flatter angles of fire to engage shipping. They fired shells up to an angle of 45 degrees, and the range of eight miles would be known as 14,080 yards by a coastal battery, though the range would actually have been greater.
This link shows a typical 9.2 inch gun mounted for shore defence. Braefoot would have had something very similar-
British 9.2"/47 (23.4 cm) Mark X