At
350 metres in length, by 50 metres wide, and encompassing a volume of
more than 260,000 cubic metres, the dock is capped at either end by
giant hollow steel gates, or caissons (shown below) each weighing in at
almost 1,500 tonnes. Capable of being filled selectively with seawater
to cope with external pressures, these 9 metre deep monsters can be
wound in and out of sockets set in the western quayside and controlled
by dedicated Winding Houses. Essentially immune from destruction by
ramming alone, it is small wonder that the initial impression of the
port's defenders was that 'Campbeltown's' attack had been little more
than a futile and costly gesture.


Aside
from the sheer scale of the caissons was the degree to which the
southern structure - 'Campbletown's' target - was dominated by nearby
German guns. Photographed from a position between cannon positions
66 and M70, on the eastern quayside, the image immediately below shows
all too clearly the height advantage enjoyed by the crews of the guns
on top of the Pumping Station roof (nos 64 and 65), who were able to
fire down on the destroyer's crowded decks at point-blank range. The
other images in the sequence demonstrate both the scale of the climb
awaiting Captain Donald Roy's assault troops - whose task it was
to access and destroy the rooftop positions - and the confusion of
galleries below the Pumping Station floor, which greeted the wounded
Lieutenant Stuart Chant and his men as they descended through the darkness to their
target impeller pumps far below.