In 1917 Germany decided to resume full unrestricted submarine warfare.

In 1916-17 he was an advocate of unrestricted submarine warfare.

There have been four major campaigns of unrestricted submarine warfare:

In the following year, unrestricted submarine warfare was trumpeted as the magic formula.

His decision not to fire on Bremen likely delayed the start of unrestricted submarine warfare.

On 18 September 1915, he called off unrestricted submarine warfare completely.

The new policy of unrestricted submarine warfare was initially a success.

This reservation needs to be made in respect to the unrestricted submarine warfare only.

In order to achieve the required results, the unrestricted submarine warfare has to commence no later than 1 February.

He also spoke in support of unrestricted submarine warfare.