(A) Chemical Weapons
(B) The machine gun
(C) Attrition Warfare
(D) ** Unrestricted submarine warfare
EXPLANATIONS BELOW
Concept note-1: -On May 6, the German government signed the so-called Sussex Pledge, promising to stop the indiscriminate sinking of non-military ships. According to the pledge, merchant ships would be searched, and sunk only if they were found to be carrying contraband materials.
Concept note-2: -The Sussex Pledge was a promise made by Germany to the United States in 1916, during World War I before the latter entered World War I. Early in 1915, Germany had instituted a policy of unrestricted submarine warfare, allowing armed merchant ships but not passenger ships to be torpedoed without warning.
Concept note-3: -…the adoption of the so-called Sussex pledge (May 4, 1916), which obliged German submarine captains to precede the torpedoing of merchant or passenger ships with a warning and to provide for the safety of passengers and crew of sunken ships in the wake of such attacks.
Concept note-4: -The Sussex Pledge and Its Aftermath↑ Germany promised to no longer attack any passenger ships, expanding the promise made in the Arabic Pledge. Merchant vessels would only be sunk if war material was aboard but only after all passengers, including the crew, had left the ship.
Concept note-5: -This ‘unrestricted submarine warfare’ angered neutral countries, especially the United States. The tactic was abandoned on 1 September 1915, following the loss of American lives in the torpedoed liners Lusitania and Arabic.