I couldn't post this with Yewgarth's plaque so perhaps Yewgarth could put the plaque here.

The cannons captured at Sebastopol, Crimean War, were presented to Birkenhead by the War Office in 1857 and originally stood near main entrance. Later they were moved to the site now known as Cannon Hill. During WW2 they were scraped and melted down to help with the war effort.

Link to the One O'clock gun.
http://www.pol.ac.uk/home/history/gun.html

So these guns were nothing to do with the one O'clock gun after all, but are directly connected with the plaque,

The chap on Yewgarth's plaque

http://en.wikisource.org/wiki/St._George,_John_(DNB00)

pic of the plaque