What two new weapons systems of the early 20th century enabled the navy to fight over and under the surface of the ocean?

Airplanes and submarines

Explanation:

Two new weapon systems that were developed in the early 20th century were airplanes and submarines. Aircraft was first used in war in 1911, but it became widespread during the Great War (1914-18). Airplanes were first used for reconnaissance, and later as fighter planes. Submarine warfare also became important during WWI, mainly as a fight between German and Austro-Hungarian U-boats.

although world war i began in 1914, the united states did not join the war until 1917. the additional firepower, resources, and soldiers of the u.s. to tip the balance of the war in favor of the allies. remaining neutral. when war broke out in 1914, the united states had a policy of neutrality.