Liverpool’s role in the Second World War (1939-1945) was crucial.  Her importance as a convoy destination was second to none in that she maintained a lifeline, with the USA and Canada , which was vital to Britain’s survival,and eventual victory.  Much of the ‘Battle of the Atlantic’ against the U-boats was indeed, fought and won from Liverpool. 
From 1941 the headquarters of Britain’s Western Approaches Command was established in the fortified basement of Derby House, Exchange Flags, Liverpool.  
From there the anti-submarine war was planned.  Pivotal to the campaign against the U-boats was the work of the Special Support Groups, composed of escort vessels such as corvettes, frigates and destroyers.  One of the most famous and successful of these groups was that based in Liverpool’s Gladstone Dock (where a plaque still hangs in its honour) and commanded by the legendary Captain ‘Johnny’ Walker.
Liverpool’s importance to the allied war effort was clear to Hitler, who ordered his Luftwaffe to ‘destroy’ the port.  
During the war, Liverpool was subjected to more bombing raids (68) than any British city outside London, the worst being the terrible 8-night ‘May Blitz’ of 1941.  
Between 1940 and 1942, nearly 4,000 Merseysiders were killed and 4,000 seriously injured in these raids, which did immense damage to the port and city.  But despite this devastation, the work of the port continued.  
As well as food and war supplies, hundreds of thousands of American and Canadian troops were transported to Britain via Liverpool in readiness for the Allied landings in Normandy, which led to the German defeat in Western Europe.
Liverpool had two other vital roles to perform in World War Two.  As the headquarters of the Battle of the Atlantic operation and as the first link in a chain of transportation and distribution of  vast quantities of equipment, food, munitions and aircraft needed for the Allied War effort.

On 10 February, USS Wakefield was recommissioned and she departed Boston on 13 April, beginning the first of 23 round-trips in the Atlantic theater, and three in the Pacific. Between 13 April 1944 and 1 February 1946, Wakefield transported 110,563 troops to Europe and brought some 106,674 men back to America - a total of 217,237 passengers. In many cases, Wakefield operated as a "lone wolf," except for air coverage a few miles out of a port. Her primary port of call in the European theater was Liverpool - visited so often in fact that the transport's crew nicknamed her "The Boston and Liverpool Ferry." The average round-trip voyage took eighteen days. After D day, 6 June 1944, Wakefield began the first of her trips as a casualty-evacuation ship, bringing home wounded GI's. On occasion, she also brought back German prisoners of war for internment in the United States.

This is a rare image of US war planes passing the Liver Buildings, at the junction of Water Street, on vehicle transporters.
They were then taken by road on transporters to Speke Airport , on the fringe of Liverpool. 
Here they were re-erected and commissioned prior to being flown to the US base at Warton near Preston for final delivery to US Air Force Bases across the Britain.

The image on the right is of Stanley Dock warehouse on the Dock Road- built in 1901 and was at the time the biggest brick building in the world.
It became the Liverpool base for the US army - Port transit Depot # 1  BADA
In conjunction with the Silcock warehouse nearby, this facility was responsible for the storage and shipment of huge quantities of food, garments, medical supplies and a thousand and one articles needed to maintain a large army at war.