(Updated September 2020) A view of the entrance to Portsmouth harbour from the saluting platform. In the foreground, two soldiers sit on the wall next to a cannon on an iron carriage and, to the right, the artist has shown a pile of cannon balls. Also, to the right, can be seen the semaphore tower flying a flag signal. Beyond to the left, lies the town of Portsmouth with the pier and Round Tower. To the left of the Round Tower is the port flagship, the 'Britannia'.
The Semaphore was the end of the early 19th-century land-line from the Admiralty in London. In 1833 it was replaced by a new tower that linked the 1778 sail loft and rigging store within the Royal Dockyard, though this may have been built a little earlier since Cooke shows it in a drawing of 1831 (see PAE5463): even this went out of use except as a dockyard signal tower after wireless telegraphy arrived in 1847. In December 1913 a major fire destroyed that tower and gutted the whole range: the present Semaphore Tower in the Dockyard is a near replica built in 1930 and with the same name, though never used for semaphore.

The artist was trained by his father the painter George Cooke, and showed outstanding talent as a draughtsman. He helped Clarkson Stanfield with some of his commissions, took lessons in oil painting from James Stark in 1834, and assisted with the arrangement of exhibits for the Great Exhibition of 1851. He exhibited at the Royal Academy 1835-79 and was made ARA in 1851, and RA in 1863. His sketchbooks are in the National Maritime Museum, London. Finden made an engraving of this painting.