And found the Anchorage on this map. 19W is located in the middle of the chart, just above HMS Vectis on the Island of Wight. So the troops were tendered out from Southampton docks to the ship. I would assume "19W/2 means the 2nd anchoring buoy at that location.
Please note that the Southampton docks, on this map are at the top, near the number 12
The second chart, shows W19 at the top right of this chart
For a clear resolution copy of the above maps, go to this link: