View from on board a collier of an East Coast Convoy: merchantmen, mostly colliers, steaming in line in the North Sea. Courtesy of Imperial War Museum. Copyright: © IWM.
By 1939, London required 40,000 tons of coal per week to generate the electricity and coal gas to power the city. Because London was the economic and industrial center of Great Britain, as well as the capital, ensuring the city received sufficient coal from coal fields in the northern part of England and Scotland was critical.
Convoy routes for colliers were designated before the war. Just a few days after war began on 3 September 1939, hundreds of ships large and small were compelled to steam up and down the Channel coast (or east coast) of England in narrow channels which were swept for mines on a daily basis.
There was no “phony war” or “bore war” for the colliers, their crews and the Royal Navy escorts which endeavored to protect them. German plans began to bomb and strafe these ships from 29 September 1939 onward. German U-boats and aircraft sewed mines up and down the coastal waters and by May 1940 these mines had accounted for most of the 114 ships sunk in British coastal waters.
Source: Coastal Convoys 1939 to 1940: the Indestructible Highway by Nick Hewitt