DHfan,
I wrote:
"....I remember reading somewhere that three of the engines had individual hydraulic pumps, each supplying one turret, so that loss of one engine would not render all turrets inoperable. But I can't find (after a cursory Google search) anything to back it up. Anybody know whether this was true ?...."
A bit more digging has turned up:
<British Power-Operated Gun Turrets - Page 2 - Axis History Forum
forum.axishistory.com/viewtopic.php?t=20042&start=15>
"....The electro-hydraulic power unit was mounted behind the gunner, giving a maximum rotation speed of 35 degrees/sec...."
So the turret movement had its own power supply (and presumably its own hydraulic reservoir), and was not dependent on the main engine-driven hydraulic system.
Which wraps it up nicely ! Danny.