In AP World, submarines are the underwater warships introduced on a mass scale during World War I that let navies sink enemy and merchant ships by surprise, an example of the new military technology in Topic 7.3 that raised casualties and helped make WWI the first total war.
Submarines are warships that operate underwater, and World War I was the first conflict where they mattered at scale. Before WWI, naval power meant big surface battleships slugging it out. Submarines broke that logic. A submerged vessel could sneak up on a battleship or a merchant ship, fire a torpedo, and disappear. There was no warning and often no defense.
Germany leaned on this hardest with its U-boat fleet, using submarines to choke off supplies headed to Britain. The strategy of unrestricted submarine warfare, sinking ships without warning, including civilian and neutral vessels, blurred the line between military and civilian targets. That blurring is exactly what the CED means when it calls WWI the first total war. Submarines sit alongside machine guns, poison gas, tanks, and airplanes as the new technologies that made WWI's casualty counts so staggering and forced both sides to invent new strategies.
Submarines live in Unit 7 (Global Conflict, 1900-Present), specifically Topic 7.3, Conducting World War I. They directly support learning objective AP World 7.3.A, which asks you to explain how governments used a variety of methods to conduct war. The essential knowledge for that objective says new military technology led to increased wartime casualties, and submarines are one of the cleanest examples. They also illustrate the Technology and Innovation theme, since they show how industrial-era engineering reshaped strategy. Bonus payoff for causation arguments. German unrestricted submarine warfare (think the Lusitania) helped pull the United States into the war, so submarines let you connect technology to diplomacy and the war's outcome in one move.
Keep studying AP World Unit 7
U-boat (Unit 7)
U-boats were Germany's submarines, the specific fleet that turned this technology into a strategy. When you write about unrestricted submarine warfare, U-boats are the concrete evidence behind the general term.
Convoy System (Unit 7)
The Allies answered the submarine threat by grouping merchant ships into escorted convoys. This is a perfect action-reaction pair for an MCQ or essay on how new tech forced new strategies on both sides.
Lusitania (Unit 7)
A German U-boat sank this British passenger liner in 1915, killing civilians including Americans. It shows how submarine warfare erased the soldier-civilian line and helped push the US toward joining the Allied Powers.
Machine Guns (Unit 7)
Machine guns did to land warfare what submarines did to naval warfare. Both belong to the same CED point that new military technology drove WWI's massive casualty levels, so they pair well as evidence.
Submarines show up most often in multiple-choice and short-answer questions about new WWI technology. Practice questions ask things like what technology was first used extensively in WWI for military purposes and how new technologies changed the strategies of both sides. Your job is not just to name the submarine but to explain its effect, that it disrupted maritime trade, raised casualties, and forced counter-strategies like the convoy system. No released FRQ has used the term verbatim, but it works as strong specific evidence for LEQs or DBQs on how governments conducted total war (LO 7.3.A) or how technology changed warfare in the 20th century. Drop it alongside machine guns and poison gas to show range across land and sea.
All U-boats are submarines, but not all submarines are U-boats. "Submarine" is the general technology used by multiple navies, while "U-boat" (from the German Unterseeboot) refers specifically to Germany's submarines in the World Wars. Say "German U-boats" when discussing unrestricted submarine warfare and the Lusitania, and "submarines" when making the broader point about new naval technology.
Submarines were one of the new military technologies of World War I that the CED says led to increased wartime casualties, supporting LO AP World 7.3.A.
Germany's U-boats waged unrestricted submarine warfare, sinking merchant and civilian ships without warning to cut off Allied supplies.
Submarine attacks on civilian targets, like the 1915 sinking of the Lusitania, blurred the line between soldiers and civilians, a defining feature of total war.
The Allies developed the convoy system in direct response to the submarine threat, showing how new technology forced new strategies on both sides.
Unrestricted submarine warfare strained Germany's relations with neutral countries and helped bring the United States into the war on the Allied side.
Submarines attacked enemy warships and, more importantly, merchant ships carrying supplies. Germany used its U-boat fleet to try to starve Britain by sinking ships headed for its ports, often without warning.
No. Submarines existed earlier, but WWI was the first war where they were used extensively and changed naval strategy. For the AP exam, the point is their first large-scale military use, not their invention.
A submarine is any underwater warship; a U-boat is specifically a German submarine (short for Unterseeboot). On the exam, U-boat signals Germany's campaign of unrestricted submarine warfare in particular.
It was Germany's policy of sinking any ship in a declared war zone, including neutral and civilian vessels, without warning. The 1915 sinking of the Lusitania is the classic example, and the policy helped draw the United States into the war.
Total war means the whole society, not just armies, becomes part of the war effort and a target. Submarines attacked civilian merchant ships and passenger liners, dragging trade and civilians directly into the fighting.
Connect this key term to the AP exam workflow: review the course, practice questions, and check related study tools.
Review units, study guides, and course resources.
Check this vocabulary in multiple-choice context.
Apply key concepts in written AP responses.
Estimate the exam score you are working toward.
Review the highest-yield facts before practice.
Put the full course together before test day.