soon learned to achieve a firing position (while avoiding the threat of enemy guns) by manoeuvring themselves behind an enemy aircraft; this is known as getting onto an aircraft's "six o'clock" or onto their "tail", plus a wide variety of other terms, usually coined by air crew. This type of combat became known as dogfighting. Oswald Boelcke, a German fighter ace during World War I, was the first to publish the basic rules for aerial combat manoeuvring in 1916, known as the Dicta Boelcke. He advised pilots to attack from the direction of the sun (toward which the defending pilot could not see), or to fly at a higher altitude than the opponent. Most of these rules are still as valuable today as they were a century ago. Today's air combat is much more complicated than that of older times, as air-to-air missiles, radar, and automatic cannons capable of high rates of fire are used on nearly all modern fighter aircraft. New and additional types of manoeuvres have emerged, intending to break radar lock by minimizing the Doppler signature of one's own aircraft ("keeping the enemy at 3 or 9 o'clock"), or to exhaust the kinetic energy of an incoming missile (by changing the aircraft's course from side to side, the missile, not flying directly at target but trying to forestall it, will make sharper turns and will eventually have to fly a longer path). However, close-range fighting with infrared guided missiles and aircraft cannons still obeys the same general rules laid down in the skies over Europe in the early 20th century. The master rule is still the same: do not let your opponent get onto your six, while attempting to get on theirs. Close-range combat tactics vary considerably according to the type of aircraft being used and the number of aircraft involved. Tactics There are five things a pilot must remain aware of when contemplating aerial engagement; of these, seeing and keeping sight of one's opponent are the most important. In Southeast Asia, over 85 percent of all kills are attributed to the attacker spotting and shooting the defender without ever being seen. Structural limitations of the attacking and defending fighters must be taken into account, such as thrust-to-weight ratio, wing loading, and the "corner speed" (the maximum or minimum speed at which the aircraft can attain the best turning performance). Variable limitations must also be considered, such