Accessible from both Basin number 4 and Basin number 5, the Prince of Wales Basin, were Dock 9 and Dock 10, the latter being adjacent to the North Lock.

This most western of the Docks measured 741 feet in length and 121 feet in width.  The depth of water over the sill at low water spring tides was 32 feet while at high water spring tides it was 47 feet 6 inches.  It was claimed that 'at almost any stage of the tide any of our warships, even laden with war stores, may pass in from the tidal (Basin 4) or the closed basin (Basin 5) to this dock.  Even if water-logged, as a result of damage in war, they could enter this dock at nearly all stages, excepting at low water'.

The entrance from Basin 4 was through Caisson J, 95 feet in width, and the entrance from Basin 5 was through Caisson P, also 95 feet wide.  Both Caissons slid into the Dock wall.  The Dock could be divided in two by the inclusion of Floating Caisson M, the north side becoming 459 feet long and the south side becoming 250 feet long.

By placing Floating Caissons at the outer stops the length of the Dock could be increased by 43 feet.