Warmatrix

The jet engine vastly increased the power of airplanes, allowing them to fly at supersonic speeds and carry much heavier payloads then before.
The defining part of a jet aircraft is its jet engine. The first such engines were turbojets. In them, air is sucked in at the front, compressed, mixed with fuel and ignited, then expelled at the rear with a higher speed than at the intake, creating forward thrust. While propellers are limited to subsonic speeds because of rapidly increasing drag when nearing the speed of sound, jet engines can function even at supersonic speeds.
The turbojet engine was invented in the 1930's CE, by Frank Whittle in Britain and later Hans von Ohain in Germany, independent of each other. Whittle had trouble getting adequate funding for his work and was overtaken by the Germans. The first operational jet aircraft was the Heinkel He 178 in 1939 CE. Whittle regained the initiative by succeeding making his Gloster Meteor the first production jet in 1941 CE, yet Germany had the definite military scoop with the first operational jet fighter, the Messerschmidt Me-262, three years later. Though plagued by startup troubles, it outclassed all allied fighter airplanes. But it arrived too late and in too small numbers to tip the balance in World War II. Other countries quickly followed with their own models.
The first jet aircraft had straight wings like their propeller-driven predecessors. They could fly at speeds approaching the speed of sound. Jet fighters almost fully replaced propeller fighters within a decade, but with bombers the transition was much slower. The first dogfight between jet fighters was in 1950 CE, during the Korean War, when an American P-80 shot down two North-Korean Mig-15's.
Within a few years after World War II jets appeared that had swept wings or delta wings, more suitable for high speeds. The 'area rule' was discovered and applied, eliminating many air drag problems at transonic and supersonic speeds. Afterburners were introduced, which inject extra fuel into the stream of exhaust gases, boosting power 1½x - 2x but also increasing fuel consumption about 4x, so they are suitable as short-term boosters only. As a result, after 1950 CE some jets started to break the sound barrier in level flight, though only for short periods. Regarding weapons they were equipped with onboard radar, infrared air-to-air missiles to attack with and had some countermeasures to defend themselves from them.
A competitor to the turbojet engine came to the front: the turbofan. This type of engine does not guide all air through the compressor, but part around it, driving a fan. Total thrust is the sum of that of the compressor and the fan. A turbofan is quieter, more efficient and generates less excess heat than a turbojet at speeds up to about 1½x the speed of sound. Its maximum limit is 2x - 3x the speed of sound, though at those velocities its efficiency is far less. Experimental turbofans appeared during World War II and they became widespread around 1960 CE, replacing turbojets in all but the fastest airplanes.
By that year aircraft design as a whole had become elaborate and costly, leading to a demand for fewer types that could be used in multiple roles. In response the first multi-role aircraft appeared, blurring the division between fighters and bombers. This led to innovate designs, like the F-111 Aardvark with its variable sweep wings and the first jumpjets. Other models remained specialized airplanes, like the SR-71 Blackbird, a spy plane that set a speed record of 3,500 kilometers per hour and a cruising height record of 25 kilometers. Pulse radar and later pulse-doppler radar and lasers allowed aircraft to guide their missiles to their targets; air-to-air missiles were joined by air-to-surface missiles. Radar made it possible to attack enemies beyond visual range. Some designs came to over-rely on missiles, dispensing with cannons, only to find out that they still needed them.
In the 1970's CE computers enhanced jet performance, by tracking and guiding missiles and providing terrain awareness to low-flying aircraft. The F-16 Fighting Falcon, introduced in 1974 CE, was the first jet fighter that used a fly-by-wire system. In it, the controls of the aircraft are not handled manually, but by computers that relay movements through electronic circuits. Computers, sensors and other electronics grew in importance during the last decades of the 20th century CE, giving pilots a good overview of the (aerial) battlefield, while taking the burden of handling the aircraft largely away. At the same time stealth technology made the airplanes themselves harder to detect. Combined with thrust-vectoring, modern flight computers are able to fly airplanes in ways that traditional methods can not, maneuvering in all directions and keeping airframes aloft that would be unflyable by humans alone. In the meanwhile engines continued to increase in power and efficiency, so that the latest jet fighters are able to 'supercruise', i.e. fly at supersonic speeds without engaging their afterburners.
Since their introduction, the performance of jet aircraft has increased vastly. The world's largest bomber, the Russian Tupolev Tu-160, can carry a bomb load of 40 tons and has a combat radius of 7,300 kilometers. The F-22 Raptor can supercruise at almost 2x the speed of sound. The next generation of jet aircraft may go even faster, to hypersonic speeds. But power, speed and maneuverability are just half the story. Modern military aircraft development is as much about detection versus stealth and control of the aircraft. Computers are steadily becoming more important, so that it is doubtful if the next generation will be manned by human pilots; the future is for the drones.