In 1939 the Royal Navy was the largest naval force in the world.
The massive fleet comprised 15 battleships, seven aircraft carriers, 66 cruisers, 184 destroyers and a huge number of support vessels.
The main anchorage at Scapa Flow, Orkney, was considered to be impregnable and dominated the passage between the North Sea and the Atlantic.
But, as The News’s exclusive new history of the Second World War points out, the navy in 1939 had several serious weaknesses.
Many of the battleships were old, and air power was limited to short-range aircraft.
The biggest weakness, however, was strategic overstretch.
The navy was required to protect British possessions worldwide and, although in 1939 the main threat was undoubtedly from Germany, the Admiralty was acutely aware that if Japan entered the war, the British Empire in the Far East would be very vulnerable.
This indeed proved to be the case when Japan attacked in 1941.
On the day, 72 years ago this month, that Britain declared war on Germany, a U-boat sank the liner Athenia.
The German submarines also struck two spectacular blows early in the war against the navy’s capital ships.
At sea, the aircraft carrier Courageous was torpedoed, while, in October 1939, U-47 under the command of Gunther Prien, made a daring raid into the main anchorage at Scapa Flow and torpedoed the battleship HMS Royal Oak. It sank with the loss of almost 800 sailors.
But there was a morale-boosting moment for the senior service in those early months of the war, at the Battle of the River Plate in December 1939.
The cruisers HMS Exeter, Ajax and Achilles engaged the German pocket battleship Graf Spee in the mouth of the River Plate off Uruguay.
Just three years earlier, as our picture here shows, the battleship flying the Swastika, took part in a fleet review at Spithead in the Solent.
Exeter was put out of action but the Graf Spee was damaged and withdrew into neutral Montevideo for 72 hours of repairs.
British naval intelligence managed to convince the Germans that a far bigger Royal Navy force had gathered off the South American country waiting for Graf Spee to re-emerge.
The captain, Hans Langsdorff, blew up his ship rather than face the Royal Navy again.
Then, dressed in full dress uniform and lying on the ship’s battle ensign, he shot himself.