Question

what german weapon created particular struggles for the u.s. during wwii? submarines nuclear missiles aircraft carriers

Explanation:

During WWII, German U - boats (submarines) were a major threat to U.S. shipping. They carried out unrestricted submarine warfare, sinking many Allied ships and disrupting supply lines. Nuclear missiles were not in use during WWII. Germany had few aircraft carriers and they did not pose the same level of threat as submarines to the U.S.

Answer:

submarines