The Northrop P-61 Black Widow, named for the American spider, was the first operational U.S. warplane designed as a night fighter, and the first aircraft designed to use radar.
 The P-61 had a crew of three: pilot, gunner, and radar operator.
 It was armed with four 20 mm (.79 in) Hispano M2 forward-firing cannons mounted in the lower fuselage, and four .50 in (12.7 mm) M2 Browning machine guns mounted in a remote-controlled dorsal gun turret.
Barrett Firearms Manufacturing is an American manufacturer of firearms and ammunition located in the unincorporated town of Christiana, Tennessee.
 It was founded in 1982 by Ronnie G. Barrett for the single purpose of building semi-automatic rifles chambered for the powerful .50 BMG (12.7×99mm NATO) ammunition, originally developed for and used in M2 Browning machine guns.
 Barrett began his work in the early 1980s and the first working rifles were available in 1982, hence the designation M82.
 Barrett designed every single part of the weapon personally and then went on to market the weapon and mass-produce it out of his own pocket.
 He continued to develop his rifle through the 1980s, and developed the improved M82A1 rifle by 1986.
The M16 Multiple Gun Motor Carriage, also known as the M16 Half-track, was an American self-propelled anti-aircraft weapon built during World War II.
 It was equipped with four 0.5 inch (12.7 mm) M2 Browning machine guns in a M45 Quadmount.
 2700 were produced by White Motor Company from May 1943 to March 1944, with 568 M13 MGMCs and 109 T10 Half-tracks being converted into M16s as well.
A squad automatic weapon (SAW, also known as section automatic weapon or light support weapon) is a weapon used to give infantry squads or sections a portable source of fully automatic firepower.
 Weapons used in this role are often selective fire rifles, usually fitted with a bipod and heavier barrel to perform as light machine guns. Squad automatic weapons usually fire the same cartridge as the assault rifles or battle rifles carried by other members of the unit.
 This reduces logistical requirements by making it only necessary to supply one type of ammunition to a unit.
 Squad automatic weapons are light enough to be operated by one person, as opposed to heavy machine guns such as the M2 Browning, which fire more powerful cartridges but require a crew to operate at full effectiveness.
The Northrop F-15 Reporter (later RF-61) was an American unarmed photographic reconnaissance aircraft.
 Based on the Northrop P-61 Black Widow night fighter, it was the last piston-powered photo-reconnaissance aircraft designed and produced for the United States Air Force.
 Though produced in limited quantities, and with a relatively short service life, the F-15's aerial photographs of the Korean Peninsula would prove vital in 1950, when North Korea invaded the south.
The M1 link, was the U.S. military designation for a steel disintegrating link designed for the M1917 Browning machine gun and M1919 Browning machine gun, and the .30-06 Springfield cartridge that they fired.
 A single round would hold two links together, and more could be added to make up a belt of any quantity of rounds, though for the mounted machine guns of the time, a belt of 250 rounds was most commonly used.
 As was the trend with American belt-fed firearms, as opposed to Soviet designs, belts of ammunition feed into the gun from the left side to the right.
The MAC-58 was a version of the French AA-52 machine gun chambered in .50 BMG instead of 7.62×51mm NATO.
 A few prototypes were tested and one retained for preserial production, but it never reached production due to the large quantity of US M2 Browning machine guns already in service with the French armed forces.
The M2 Machine Gun or Browning .50 Caliber Machine Gun is a heavy machine gun designed toward the end of World War I by John Browning.
 Its design is similar to Browning's earlier M1919 Browning machine gun, which was chambered for the .30-06 cartridge.
 The M2 uses the much larger and much more powerful .50 BMG cartridge, which was developed alongside and takes its name from the gun itself (BMG standing for "Browning Machine Gun").
 It has been referred to as "Ma Deuce", in reference to its M2 nomenclature.
 The design has had many specific designations; the official designation for the current infantry type is Browning Machine Gun, Cal.
 .50, M2, HB, Flexible.
 It is effective against infantry, unarmored or lightly armored vehicles and boats, light fortifications and low-flying aircraft.
 The M2 has been produced longer than any other machine gun.
The M45 Quadmount (nicknamed the "meat chopper" and "Krautmower" for its high rate of fire) was a weapon mounting consisting of four of the "HB", or "heavy barrel" .50 caliber M2 Browning machine guns (of the M2 Turret Type (TT) variant) mounted in pairs on each side of an open, electrically powered turret.
 It was developed by the W. L. Maxson Corporation to replace the earlier M33 twin mount (also from Maxson).
 Although designed as an anti-aircraft weapon, it was also used against ground targets.
 Introduced in 1943 during World War II, it remained in US service as late as the Vietnam War.
The Marmon-Herrington Combat Tank Light Series were a series of American light tanks/tankettes that were produced for the export market at the start of the Second World War.
 The CTL-3 had a crew of two and was armed with two .30 cal (7.62 mm) M1919 machine guns and one .50 cal (12.7 mm) M2 Browning machine gun.
 They were originally designed to be amphibious light tanks.
 They were rejected by the U.S. Marine Corps in 1939, but after the attack on Pearl Harbor they were exported and used as an emergency light tank.

Question: The Northrop F-15 Reporter was based on a night fighter that included how many mounted M2 Browning machine guns?
Answer: four