IF you can get a copy from your library (whilst it's still there), try and get "Walls of War" by Keith Mallory & Arvid Ottar. Pub
. Astragel Books. ISBN 0 906525 14 4. This shows the details of the Thames Forts which were built to same design as the Mersey Forts.
Shows the construction, plans etc. Conditions aboard weren't a barrel of laughs.
To be hit by a WW2 torpedo, it would have to be a "lucky" shot.