One area that underwent tremendous technological development was aircraft. Planes in 1914 are made of balsa wood and doped canvas, and changed course by wing warping - the rather frightening concept of bending your wings to roll the aircraft. Few planes could pass 100mph, and most risked falling apart if they so much as came close to those kinds of speeds. Aviation design was part-science, part-guesswork, and scores of different aircraft were introduced throughout the war, with British squadrons typically not having consistent same-model flights until the formation of the RAF in 1918. In the first half of the war you have planes with anywhere from one to three sets of wings, no set engine position, no set propellor position, no way to safely fire machine guns through propellors (for the French and British.)
Though there are no truly 'great' aircraft from the era - no WW1 aircraft was truly viable by 1939, whereas the Lancaster bomber was used by the RAF through to 1990 in its 'Shackleton' variant - the progress designers made was huge. Wing warping gave way to ailerons and elevators, engines became more powerful and efficient, and German designers even begin to introduce metal-bodied aircraft by 1918, the Junkers J9. Though there is still a great deal of experimentation and variation in different aircraft by 1918 WW1 has effectively created a standardised fighter or 'scout' design, with all the primary aircraft of the major powers looking relatively similar. In effect the war was a bloody testing ground for the 'growing pains' of aviation that may not have been possible in peacetime.
Principle source: James Hamilton-Paterson's 'Marked for Death' 2015
Edit: Grammar and punctuation fixes.
Aircraft, tanks, automatic weapons, radio communication, chemical warfare, and warfare logistics underwent important advances in the span of 4 years or less. Lets first look at aircraft design and their inclusion of automatic weapons and radio communication.
/u/thekev506 introduced some of the basic changes in aircraft design, however aircraft design was experiencing something of a renaissance in the years leading up to the war. For example, consider the environment in which aircraft operate. How does one measure the speed of a moving body when you don't have a fixed reference? How does one measure altitude, wind speed/direction and atmospheric pressure? How do you find location when you can't even see the ground, such as in cloud cover? How do you navigate (relative to the ground) when you have to contend with wind direction and speed (relative to the air)? Pilots, designers, and engineers had to figure all of this out on the fly (zing).
Advances in aircraft roles required very real advances in fighter/bomber design and tactics. According to Robert Grattan, author of The Origins of Air War: "At the outbreak of war, aircraft were used principally for reconnaissance... As new roles, such as bombing and air fighting emerged, the aircraft design had to become more specialized." Aircraft began to be built for a specific purpose, rather than meeting the basic requirement of not falling apart in midair. Fighters developed more of a lightweight racing design, sacrificing weight and armor for maneuverability and speed. Bombers sacrificed maneuverability and rate of climb for armor, armament, and range. Even shipborne aircraft, and their need for folding wings, were being designed as early as 1911, including a patent for folding wings filed by the Short Brothers in 1913. (Driver, The Birth of Military Aviation)
Advances in aircraft design were not always equal. The first fighter to feature an interrupter gear (a synchronizing gear allowing the machine gun to fire through a propeller), the German Fokker E1 Eindekker, led to the period known as the "Fokker scourge" in 1915, until the British and French could copy (literally) the design. Grattan characterizes the advances of aircraft development during 1914-1918 as
Radio communication also underwent significant technological advancements during the war. Wireless communication during the outbreak of war was relatively rudimentary, and the first wireless sets were upwards of 80 lbs. By 1916, this weight was reduced to 20 lbs, and wireless transmissions became more common (so much so that the German army began jamming wireless signals.) In fact, tactics including radio directional finding were first used during WW1 by the British, by using "compass" stations to locate German aircraft radio transmissions and track their vector and position. This tactic, in conjunction with radar, would evolve with devastating efficiency during the Battle of Britain in WW2.
As airplanes evolved from reconnaissance aircraft into fighters and bombers, the need for defensive and offensive armaments arose. Up until the invention of the interrupter gear, there was a serious design limitation in most frontline fighter aircraft: the engine placement on the nose. This was overcome by either placing the engine in the rear of the cockpit ([Vickers F.B.5] (https://en.wikipedia.org/wiki/Vickers_F.B.5#/media/File:Vickers_FB.5_Gunbus_2345_G-ATVP_Yvtn_09.07.66_edited-3.jpg), a design known as a "pusher plane") or placing the machine gun above or below the cockpit, and set to fire at a harmonization angle (Nieuport 11/16). The invention and widespread use of the interrupter gear then allowed forward firing machine guns on fighter planes, increasing their efficiency and use throughout the battlefield. Rear facing machine guns were under no such limitation, and swivel designs were relatively common in bomber aircraft. As the war progressed, machine gun caliber and reliability increased, making aircraft more deadly, which necessitated new fighter and bomber tactics.
