In the early years of the 20th century the Royal Navy underwent a major programme of modernisation which resulted in its ships and men being divided into three equal divisions – each based on one of the home Royal Dockyards – Chatham, Portsmouth and Plymouth. Chatham returned to being a fleet base. New shore-based naval barracks were built alongside each of the three dockyards.
At Chatham, the new Royal Naval Barracks were named HMS Pembroke and built to the east of the Victorian Dockyard extension. By the outbreak of the First World War some 205 ships were manned by Chatham Division men – and saw action across the world- both on sea and on land. The first shot of the naval war was fired by a Chatham Division destroyer HMS Lance in the North Sea and Chatham division ships bore the brunt of naval casualties at sea in the first months of the war. These included the loss of three Chatham cruisers, HMS Hogue, Aboukir and Cressy, sunk together on the morning of the 22nd September 1914 by a single German submarine – the U-9 . Chatham division ships fought at Jutland in May 1916 and Chatham division men took part in the Zeebrugge Raid in April 1918. On land the Chatham Division provided men for the Royal Naval Division which fought gallantly and with great loss of life at Gallipoli in 1915 and on the Somme in 1916. The names of over 8,000 men of the Chatham Division who lost their lives during the First World War and for whom there is no known grave are commemorated on the Chatham Naval Memorial which stands above the Historic Dockyard on the Great Lines.
The Chatham Division saw action again throughout the Second World War – with the Chatham manned cruiser HMS Ajax leading the South Atlantic Squadron at the Battle of the River Plate and HMS Sheffield taking part in the hunt for the Bismarck, numerous Mediterranean convoys and action in the Arctic supporting Russian bound convoys.
In 1956, as the Navy became much smaller, divisional manning was replaced by Central Manning – thereafter Chatham became home to the reserve – or standby fleet, although a number of operational ships were also based at the Dockyard including the Antarctic patrol vessel HMS Endurance.