(A) Submarinesattacked unarmed ships
(B) Armoredtanks crossed fortified lines
(C) ** Theuse of machine guns resulted in massive casualties
(D) Airplanes conducted reconnaissance missions
EXPLANATIONS BELOW
Concept note-1: -The defensive power of the machine gun created the stalemate on the Western Front, and almost all of the technologies that were introduced during the war were built in order to defeat it. The introduction of this weapon radically changed the strategies and tactics used by militaries in the future.
Concept note-2: -Answer and Explanation: The single most important invention to break the stalemate of trench warfare in World War 1 was the armored tank. The tank provided soldiers with cover from enemy fire and the ability to advance over open ground. They first appeared in 1916.
Concept note-3: -World War I popularized the use of the machine gun-capable of bringing down row after row of soldiers from a distance on the battlefield. This weapon, along with barbed wire and mines, made movement across open land both difficult and dangerous. Thus trench warfare was born.
Concept note-4: -Back on the ground, the tank proved to be the answer to stalemate in the trenches. This British invention used American-designed caterpillar tracks to move the armored vehicle equipped with machine guns and sometimes light cannon.