During WWI, the Germans were the first to employ flamethrowers. Their flamethrowers could shoot flame jets up to 130 feet (40 m).¹⁾

WWI included about 65 million men from 30 countries. Almost ten million people died. The Allies (Entente Powers) lost around 6 million men. The Central Powers lost around 4 million people.²⁾

During WWI, over two-thirds of all military casualties occurred in battle. In earlier battles, sickness was the leading cause of death.³⁾

German forces shot and murdered 150 people in Aerschot in August 1914. The assassination was part of a war doctrine known as Schrecklichkeit (“fearfulness”). Its goal was to frighten inhabitants in occupied regions so they would not resist.⁴⁾

During WWI, British tanks were divided into “males” and “females”. Male tanks were armed with cannons, whereas female tanks were armed with heavy machine guns.⁵⁾

During WWI, “Little Willie” was the first prototype tank. It was built in 1915 and could go at speeds of up to 3 mph (4.8 km/h).⁶⁾

The artillery barrage and mines made a tremendous amount of noise. Explosives exploding behind the German lines on Messines Ridge in Ypres, Belgium, could be heard 140 miles (220 kilometers) distant in London in 1917.⁷⁾

The Pool of Peace is a 40-foot (12-meter) deep pool in the Belgian town of Messines. It plugs a hole left by the British detonation of a mine holding 45 tons of explosives in 1917.⁸⁾

Manfred Albrecht Freiherr von Richthofen (1892-1918), also known as the “Red Baron,” was the most successful fighter pilot of the whole war. He downed more planes than any other WWI pilot. He was killed after being shot near Amiens. René Fonck (1894-1953) of France was the Allies' most successful fighter pilot, downing 75 enemy aircraft.⁹⁾

Dogs were deployed as messengers during WWI, carrying orders to the front lines in capsules connected to their bodies. Telegraph wires were also laid down by dogs.¹⁰⁾

Big Bertha was a 48-ton German cannon used during WWI. It was named after the designer's wife, Gustav Krupp. It could shoot a 2,050-pound (930-kg) shell 9.3 kilometers (15 km). However, assembling a workforce of 200 workers takes at least six hours. Germany possessed 13 of these massive cannons, dubbed “wonder weapons”.¹¹⁾

Tanks were originally referred to as “landships”, but in order to disguise them as water storage tanks rather than weapons, the British opted to code name them “tanks”.¹²⁾

Just before his death, French Second Lieutenant Alfred Joubaire wrote in his journal regarding WWI, “Humanity is mad! It must be mad to do what it is doing. What a massacre. What scenes of horror and carnage! I cannot find words to translate my impressions. Hell cannot be so terrible! Men are mad”!¹³⁾

Some Americans were dissatisfied with the United States' initial unwillingness to enter WWI, so they enlisted in the French Foreign Legion, the British army, or the Canadian army. The Lafayette Escadrille, which was part of the French air force and became one of the premier combat units on the Western Front, was founded by a group of American pilots.¹⁴⁾

British cryptographers decoded a message from German Foreign Secretary Arthur Zimmermann to Germany's minister in Mexico in early 1917. The message urged Mexico to attack American territory. For more than a month, the British kept it hidden from the Americans. They intended to reveal it to the US at the opportune time to entice the US to join them in the fight.¹⁵⁾

“He kept us out of war,” was Woodrow Wilson's campaign slogan during his second term. On April 6, 1917, just a month after assuming office, the United States declared war on Germany.¹⁶⁾

In May 1917, Congress approved the Selective Service Act, generally known as the conscription or draft, to augment the size of the United States Army during WWI.¹⁷⁾

During WWI, persons of German ancestry were suspected in the United States. Some anti-German riots were violent, involving the burning of German publications and the death of one German-American.¹⁸⁾

During WWI, the Spanish flu killed around one-third of all military personnel.¹⁹⁾

Herbert Hoover, who would go on to become President in 1929, was appointed as the United States Food Administrator. His task was to supply food to the United States army and its allies. He urged people to build “Victory Gardens,” sometimes known as personal gardens. More than 20 million Americans established their own gardens, while food consumption fell by 15% in the United States.²⁰⁾

WWI cost the United States more than $30 billion.²¹⁾

Thousands of troops were scarred or crippled as a result of the battle. Masks were employed to conceal the most hideous deformities, but reconstructive surgery was utilized to restore face damage. Some veterans spent their whole lives in nursing facilities.²²⁾

WWI is the world's fifth bloodiest conflict.²³⁾

T.E. Lawrence (1888–1955), a British novelist better known as Lawrence of Arabia, served as an Allied spy in the Middle East. Additionally, he led an uprising of Arabs against the Turks, which he described in his book The Seven Pillars of Wisdom.²⁴⁾

Following World War I, the Ottoman, Austro-Hungarian, German, and Russian empires all fell.²⁵⁾

The Continental Army utilized the first military submarine (called the Turtle) during the American Revolution, but it wasn't until Germany's fleet of U-boats was deployed during World War I that submarines had a significant military influence. Its submarines typically remained above the waterline and only dove underwater to launch torpedoes at ships. One of the main causes the U.S. entered the conflict was Germany's indiscriminate submarine warfare.²⁶⁾

The Great War, the World War, the War of the Nations, and the War to End All Wars were other names for World War I.²⁷⁾

Between 1914 and 1918, nearly every continent and every ocean saw combat during World War I. However, the most of the combat occurred in Europe.²⁸⁾

The shooting deaths of Archduke Franz Ferdinand, the heir to the Austro-Hungarian monarchy, and his wife on June 28, 1914, signaled the start of World War I. On July 28, 1914, Austria-Hungary formally declared war on Serbia. Germany backed Austria-Hungary, whereas Russia, France, and Germany supported Serbia. The violence rapidly spread to other nations throughout the world.²⁹⁾

During World War I, Russia mobilized 16 million men, making it the war's greatest army. More over 3/4 were lost during combat—dead, injured, or missing.³⁰⁾

Black Hand, Sarajevo was the terrorist organization responsible for the death of Franz Ferdinand.³¹⁾

The United States entered WWI during the final year and a half of the war.³²⁾

Between 1914 and 1918, 274 German U-boats sunk 6,596 ships. U-35 (sank 224 ships), U-39 (154 ships), U-38 (137 ships), U-34 (121 ships), and U-33 were the five most successful U-boats (84 ships). The majority of them were sunk along the coast, especially in the English Channel.³³⁾

German trenches contrasted sharply with British trenches. Bunk beds, furnishings, cabinets, water tanks with taps, electric lights, and doorbells were all incorporated in German trenches.³⁴⁾

During WWI, France, not Germany, was the first to employ gas on opposing soldiers. They used the first tear gas grenades (xylyl bromide) against the Germans in August 1914. Germany initially employed tear gas against Russian soldiers in January 1915, but the gas turned to liquid in the chilly air. The Germans were the first to employ toxic chlorine gas in April 1915.³⁵⁾

During WWI, the Germans discharged around 68,000 tons of gas, and the British and French released 51,000 tons. In total, 1,200,000 troops on both sides were gassed, with 91,198 of them dying horribly.³⁶⁾

In an emergency of contact with gas, soldiers were instructed to cover their faces with a urine-soaked cloth.³⁷⁾

By 1918, gas masks with filter respirators were typically adequate protection.³⁸⁾

Following the end of the war, numerous countries signed treaties prohibiting the use of chemical weapons.³⁹⁾

During the war, the United States transported over 7.5 million tons of supplies to France to aid the Allied cause. There were 70,000 horses or mules, roughly 50,000 vehicles, 27,000 freight cars, and 1,800 locomotives among them.⁴⁰⁾

WWI saw the widespread usage of the machine gun, which Hiram Maxim invented in the United States in 1884. The water-cooled Maxim weighed roughly 100 pounds. It could shoot between 450 and 600 rounds per minute. The Maxim design was employed in the majority of machine guns used in WWI.⁴¹⁾

During WWI, the phrase “dogfight” was created. The pilot had to cut off the plane's engine on occasion to prevent it from stalling when the plane twisted fast in the air. It sounded like dogs barking as a pilot ignited his engine in flight.⁴²⁾

The French used what German soldiers referred to as the Devil Gun. This 75 mm gun was accurate up to 5 miles. The French generals declared that the Devil Gun had won the war.⁴³⁾

During the United States' engagement in WWI, more than 75,000 persons delivered around 7.5 million four-minute pro-war speeches in movie theaters and elsewhere to an estimated 314.5 million people.⁴⁴⁾

American troops referred to them as “Hello Girls”, and they were American women who worked as telephone operators for Pershing's army in Europe. The women spoke fluent French and English and had received special training from the American Telephone and Telegraph Company.⁴⁵⁾

The United States Army ultimately awarded military honors and veteran benefits to the few remaining Hello Girls in 1979.⁴⁶⁾