Today (4th February) in 1915, the German government announced that it would impose a submarine blockade of Great Britain with effect 18th February 1915. It meant that any shipping, including that of neutrals, could be sunk without warning. Until this change in policy, German submarines, as with those of the Allies, had surfaced in the vicinity of merchant ships and given the crews time to take to their boats in safety before sinking the ships. The introduction by Britain of ‘Q’ ships caused a rethinking of the policy.
Another significant factor in bringing about the change was Britain’s tightening of its naval blockade of Germany in November 1914. From then on, and controversially, foodstuffs were declared contraband goods and liable to seizure by the Royal Navy. This angered Germany who rightly saw it as an attempt to starve the country into submission. Indeed, the strategy was hugely successful and contributed to the ending of the war four years later.
Unsurprisingly, the policy angered the neutral states and in particular the US. The sinking of the British-owned Lusitania in May 1915, however, did not bring the US into the war with the Allies as many people believe. Several American lives were lost and this had the effect of turning US public opinion against Germany, but the US didn’t enter the war until 1917. Even so, in late August 1915, Germany dropped its campaign of unrestricted submarine warfare in the face of the backlash by neutral countries.
It was not until 1st February 1917 that Germany re-established its campaign of unrestricted submarine warfare. It was highly successful and, but for changes in the Royal Navy’s tactics and improvements in anti-submarine technology, might well have brought Britain to its knees. This time the Germans were well aware that the new campaign might bring the US into the war and, accordingly, in January 1917 the German Foreign Secretary, Arthur Zimmerman, sent a secret telegram to his Mexican Ambassador. In it he ordered an approach to the Mexicans with a proposal to fund them in a campaign to invade the US and reconquer the states of Texas, New Mexico and Arizona. The rationale for this was that it would keep the Americans too busy in their own back yard to involve themselves in Europe.
Fortunately, this telegram was intercepted by the Royal Navy and its contents cleverly leaked to the US, bringing about their entry into the war on the Allied side. However, that forms part of a plot in a later book of mine, so I will skip the details!