The Treaty of Versailles had imposed severe restrictions upon Germany constructing vehicles for military purposes, and so throughout the 1920s and 1930s, German arms manufacturers and the Wehrmacht had begun secretly developing tanks . As these vehicles were produced in secret, their technical specifications and battlefield potentials were largely unknown to the European Allies until the war actually began. When German troops invaded the Benelux nations and France in May 1940, German weapons technology proved to be immeasurably superior to that of the Allies .
The United Kingdom relied heavily on imports to feed its population and supply its war industry, and the German Navy hoped to blockade and starve Britain using U-boats to attack merchant ships in unrestricted submarine warfare . This struggle between German submarines and British counter measures became known as the " First Battle of the Atlantic ". As German submarines became more numerous and effective, the British sought ways to protect their merchant ships. " Q-ships ", attack vessels disguised as civilian ships, were one early strategy.