Why did germany use u boats to attack neutral countries?

Germany wanted to defeat Britain. So, it used U-boats.

Explanation:

Germany's most challenging naval weapon was the U-boat. Germany resumed unrestricted submarine warfare in World War 1 as they wanted to defeat Great Britain. They wished to win the war before France and America would enter the war.

The Germans lost 178 U-boats during this war, but it was successful in sinking 5,000 ships. Germany had publicly declared that they destroy all enemy merchant vessels around Great Britain with their submarines. They sank three American merchant vessels. This resulted in U. S. declaring war on "Germany" in April 1917.