In contrast, five months of submarine warfare against cruisers would bring about a decrease in tonnage to England of only 5 x 400,000 tons, even if submarines were allowed to sink all armed ships. This is approximately 18% of the present monthly maritime traffic, that is to say, less than half of what would be accomplished by unlimited submarine warfare. Based on our previous experiences, allowing submarines to sink all armed ships would probably not bring about a considerable increase in sunken freight tonnage in comparison with the approximately 400,000 tons achieved in the last two months. In all probability, it would only compensate for the decline that is to be otherwise expected as a result of the continuing arming of ships. Of course, even the removal of about one-fifth of the present English maritime traffic would have a very disturbing effect on the provisioning of England. I can rule out the possibility, however, that an England under the utterly determined present leadership of Lloyd George would be led by this to sue for peace, especially as the effects of the scarcity of fat, wood, and ore, as mentioned above, and the sustained impact on the supply of munitions would not occur. Moreover, the psychological effects of panic and horror would not set in. These effects, which are to be obtained only from unlimited submarine warfare, are, I think, an indispensable precondition for success. How important they are is shown by the experiences we had with submarine warfare at the beginning of 1915, when the English still believed in its seriousness and even in the short submarine warfare of March and April 1916.
Another precondition for success is that the beginning and the announcement of unlimited submarine warfare must coincide in such a way that leaves no time for negotiations, especially between England and the neutral nations. Only in this case will a holy fear be put into the enemy and the neutral nations.
Announcing unlimited submarine warfare will once again force the government of the United States to answer the question of whether or not it wants to act on the position it has taken on submarine warfare up until now. I am very much of the opinion that war with America is such a serious matter that everything must be done to avoid it. In my opinion, however, the aversion to this break must not lead us to shrink from using, in the decisive moment, the weapon that promises us victory.
In any case, one should plan for the worst and get a picture of the influence America’s joining our enemies would have on the course of the war. In regard to shipping capacity, this influence can only be very small. It is not to be expected that more than a small percentage of the tonnage of Germany and its Allies in American or other neutral harbors could be quickly put into service for the trip to England. By far the largest part could be damaged in such way that it would not be able to travel in the first months. The preparations for this have been taken. There would also be no crews for these ships at first. Just as little decisive impact can be attached to American troops – who, on account of limited freight capacity, cannot be brought over in considerable numbers – and American money, which cannot make up for insufficient technical supplies and tonnage. The only remaining question is how America would respond to a peace such as England would be required to make. It is unlikely that America will then decide to continue to fight us alone, as America will have no means with which to harm us significantly, whereas its ocean traffic will be damaged by our submarines. On the contrary, it is to be expected that America will join England in signing the peace treaty in order to return its economy to a healthy state.
I therefore conclude that an unrestricted submarine warfare initiated soon enough to bring about peace before the world harvest in summer 1917 – that is, before August 1 – must hazard the consequences of a break with America, for no other choice remains to us. Despite the danger of a break with America, unlimited submarine warfare, begun soon, is the right means for ending the war successfully. It is also the only means to reach this goal.