Karl Fairburne is not a real person. More importantly, Sniper Elite's protagonist was not even based on any one, notable American/British sniper or individual of the Second World War, quite simply, because there wasn’t any.
Back in the first half of the 20th century, the concept of a single soldier highly experienced in long distance engagements was drastically undervalued. While there had been many marksmen during the American Revolutionary War, and the British established the first official sniper unit in history (complete with ghillie suits) after the Second Boer War, those regiments were always disbanded after the cessation of hostilities. No nation kept and trained sharpshooters on a regular basis, as weapons were simply not powerful nor accurate enough to reliably hit a target over long distances to warrant a specialised unit.
As technology advanced, Franz Ferdinand was murdered, and Germany invaded Belgium, the situation started to change. During the First World War, Germany employed snipers that absolutely devastated the Allied forces. German sharpshooters were the only troops on either side of the conflict equipped with scoped sniper rifles, granting them an obvious advantage in a warfare method that involved poking your head up off a trench to shoot at people.
The French and British at first believed such hits to be coincidental, until the German scoped rifles were discovered. Soon after, the British army began to train their own snipers in specialised sniper schools, and the "First Army School of Sniping, Observation, and Scouting" was founded at Linghem, France in 1916, with a first class of only six people. Major Hesketh Hesketh-Prichard (really) started training those new recruits and many more during the next few years, and helped develop many of the modern techniques in sniping, including the use of spotting scopes, working in pairs, and using Kim's Game to train observational skills.
When the war ended, most nations dropped their specialised sniper units (including the Germans), because humans are stupid. During the 1930’s, the only nation that had specially trained sniper units was the Soviet Union, who not only trained their skills as marksmen, but also taught them to use the terrain to hide themselves from the enemy and to coordinate and work alongside regular forces. This made the Soviet sniper training focus on more “normal” combat situations than those of other nations, and would eventually influence the sniper training of modern times.
In 1939, the seasons changed. Springtime for Germany and winter for Poland and France reignited the unfortunately constant fire of war that ravages Europe, and snipers once more gained prominence to military eyes. During the 1940’s campaigns, lone, well-hidden French and British snipers could halt the German advance for a significant amount of time, prompting the British to once again increase their training of specialised sniper units. Drawing from the Soviet book of snipin’, British snipers were trained to blend in with the environment, usually by wearing special camouflage clothing for concealment, but the British Army offering of sniper training exclusively to officers and non-commissioned officers resulted in a very small number of trained snipers, and consequently, a considerable reduced overall effectiveness.
In 1941, the U.S. joined the war, and unlike the European nations, they hadn’t really participated in a conflict of big proportions in the recent years (they only joined WWI at the last year). In the United States Armed Forces, sniper training was basic, mainly concerned with hitting targets over long distances (specifically, a body over 400 meters away, and a head over 200 meters away). During Operation Torch in North Africa (helloooo Sniper Elite III), most fighting occurred in arid and mountainous regions with very little potential for concealment, which made training about blending into the environment virtually non-existent. It wasn’t until until the Normandy Invasion in 1944 that the U.S. would care about proper sniper concealment, and even then, they didn’t really started to give a damn about snipers until the Vietnam War.
As a result, there was no notable U.S. sniper during the Second World War. There were barely any U.S. snipers at all. Yep, that’s right: that guy with a scoped rifle you saw sniping Germans in Saving Private Ryan? He was not an actual sniper; he was a designated marksman. And there is an important difference between a sniper and a marksman.
You see, snipers are lone wolfs. They usually operate alone or in pairs, and they are always detached from the main force. Snipers are something called a force multiplier, a military concept where the whole is greater than the sum of its parts. When the 300 Spartans (and 7000 other Greeks) used the narrow valley of Thermopylae to hold off the 450,000 strong Persian army, the terrain topography acted as a force multiplier -- in this case, it allowed the Spartans to engage an enemy force 60 times its size.
In the case of a sniper, a single individual hidden in an advantageous firing position far from battle and carrying a high powered rifle also acts as a force multiplier, severely augmenting the effectiveness of an army or offensive when compared to the regular value of a single normal soldier. One sniper alone is worth multiple squads or even a whole platoon, and their deployment as intel gatherers and long range shooters is of utmost importance to military engagements; they are often tasked with responsibilities other than delivering long-range fire, such as conducting reconnaissance and directing artillery barrages or airstrikes.
On the other hand, a marksmen is a person skilled in precision shooting who is not expected to operate independently of a parent unit. In the U.S. Army, they’re known as SDM (Squad Designated Marksman) and are always attached to a fireteam composed of four or less members, serving to extend the reach of the squad and neutralise valuable targets as needed. So a sniper is always a marksman, but a marksman is not always a sniper.
The American forces had several marksmen in its ranks, but very few bonafide snipers. Although the U.S. Army didn’t recognised the concept of a single qualified specialist capable of providing discriminatory, highly-accurate rifle fire against enemy targets as something valuable, their intelligence services certainly did.
The Office of Strategic Services (OSS) was a wartime intelligence agency of the United States during World War II, focused on coordinating espionage activities behind enemy lines for all branches of the United States Armed Forces. Their duties involved the acquisition of intelligence, sabotage of enemy war efforts, and the elimination of targets. The OSS was disbanded in 1945 and restructured as the CIA (Central Intelligence Agency) in 1947.
The SOE (Special Operations Executive) was its British World War II equivalent, focused on conducting espionage, sabotage, and reconnaissance in occupied Axis territories. They aided and funded local resistance movements in occupied countries to rise up against Axis powers, and frequently collaborated with the OSS in joint missions. If the OSS was the shooting secret agent, the SOE was the sneaky bastard that turns off the alarm, riles up the peasants, and sets fire to things.
Karl Fairburne is an American OSS operative working in conjunction with the SOE, meaning he is one awesome son of a bitch. As an OSS agent, he would be focused on the military infiltration of highly secure locations and the elimination of targets and assets. That’s where the plot for Sniper Elite V2 and the sniper part of his job comes from. As an SOE operative, he would perform works of espionage, subversion, and support, gathering intel and undermining Nazi control of occupied regions while paving up the way for military offensives. That’s why the plots for Sniper Elite III and 4 happen.
This premise for the character’s role actually fits within the profile of wartime agents, and provides a brilliant little way to justify his myriad of assignments and considerable freedom on the job.
In the British Army, each sniper was given considerable latitude in what they wore and how they worked; it all depended on circumstances of terrain, mission, and weather. As a commando and unlawful combatant operating outside “normal” warfare, Karl’s rules of engagement were even more lax. His loner persona explains his penchant for infiltrating highly secure enemy positions and killing people, while his missions gave him significant freedom in approaching the special operations assigned to him by Allied intelligence.
In real life, snipers were not part of the usual contingent of intelligence services’ agents, since organisations preferred a more subtle approach than “loud gun goes boom and someone’s head explodes”, but they definitely valued the expertise of a talented sharpshooter every now and then. The fact Karl was not dead -- something that happened a lot in sniper ranks due to the constant deployment behind enemy lines and aforementioned lack of subtlety -- certainly put him pretty high up in the list of “good snipers we can rely on to get the job done”, and could conceivably lead to a scenario where he would be brought in full time to assist Allied intelligence efforts.
Given Karl’s focus on sniping people from a distance and his absolute refusal to ever camouflage, we can conclude that Karl was an U.S. trained sniper. British trained ones learned to blend with the environment and used camouflaged gear such as ghillie suits to attain further concealment. Karl doesn’t, and instead acts as a lone operative that infiltrates highly secure locations, acquires intel, and sabotage Nazi facilities -- all while stabbing and shooting people. This long range, adaptable skill set contrasts severely with the British focus on speciality training, and paints Karl as an American commando.
However, his missions were often assigned by the SOE, as seen in his support role assisting the British forces in North Africa during the Battle of Gazala at the beginning of Sniper Elite III, and his nature as an operative fomenting the Italian resistance in Sniper Elite 4. These operational directives focused on aiding the war effort by attaching a sniper to offensives and insurrections instead of placing him as an organic part of a fireteam, indicating clear British handiwork behind his assignments. That close relationship with the SOE could also indicate why a lot of Karl’s gear and close combat manoeuvres are British.
So, based on all the information available in the game, and comparing that to all the historical data we have, we can confidently confirm that Karl Fairburne is as an OSS operative working in conjunction with the SOE. His large range of proficiencies and skill with a sniper rifle indicates an U.S. sniper origin, while his equipment and close combat training indicates a tiny bit of British influence. Rebellion’s historical concept for the character is spot on, unexpectedly flexible, and surprisingly well developed -- so while there were no real Karl Fairburnes in the history of World War II, there very well might have been.