The 10.5 cm SK L/45 ("Schnelladekanone Länge 45", quick-loading cannon with a barrel length of 45 calibers) was a German naval gun that was used in World War I and World War II and was the successor of the older 10.5 cm SK L/40 naval gun.
The 5"/25 caliber gun (spoken "five-inch-twenty-five-caliber") entered service as the standard heavy anti-aircraft (AA) gun for United States Washington Naval Treaty cruisers commissioned in the 1920s and 1930s.
 The goal of the 5"/25 design was to produce a heavy AA gun that was light enough to be rapidly trained manually.
 The gun was also mounted on pre-World War II battleships and aircraft carriers until replaced by the standard dual-purpose 5"/38 caliber gun, which was derived from the 5"/25 and was similar except for the barrel length.
 Guns removed from battleships were probably converted for submarine use by late 1943, while a purpose-built variant for submarines was available in mid-1944, and was widely used by them.
 United States naval gun terminology indicates the gun fired a projectile 5 inches (127 mm) in diameter, and the barrel was 25 calibers long (that is, for a 5" bore and a barrel length of 25 calibers, 5" x 25 = 125", or about 3.2 meters).
The Mark 42 5"/54 caliber gun (127mm) is a naval gun (naval artillery) mount used by the United States Navy and other countries.
 It consisted of the Mark 18 gun and Mark 42 gun mount.
 United States naval gun terminology indicates the gun fires a projectile 5 in in diameter, and the barrel is 54 calibers long (barrel length is 5" × 54 = 270" or 6.9 meters.)
 In the 1950s a gun with more range and a faster rate of fire than the 5"/38 caliber gun used in World War II was needed, therefore, the gun was created concurrently with the 3"/70 Mark 26 gun for different usages.
 The 5"/54 Mk 42 is an automatic, dual-purpose (air / surface target) gun mount.
 It is usually controlled remotely from the Mk 68 Gun Fire Control System, or locally from the mount at the One Man Control (OMC) station.
Gustav Krupp von Bohlen und Halbach (7 August 1870 – 16 January 1950) ran the German Friedrich Krupp AG heavy industry conglomerate from 1909 until 1941.
 He and his son Alfried would lead the company through two world wars, producing almost everything for the German war machine from U-boats, battleships, howitzers, trains, railway guns, machine guns, cars, tanks, and much more.
 Krupp produced the Tiger I tank, Big Bertha, the Paris Gun, among other inventions under Gustav.
 Following the war, plans to prosecute Gustav Krupp as a war criminal at the 1945 Nuremberg Trials were dropped because by then he was bedridden and senile.
The 3"/23 caliber gun (spoken "three-inch-twenty-three-caliber") was the standard anti-aircraft gun for United States destroyers through World War I and the 1920s.
 United States naval gun terminology indicates the gun fired a projectile 3 inches (76 mm) in diameter, and the barrel was 23 calibers long (barrel length is 3" x 23 = 69" or 1.75 meters.)
The 14 cm/40 11th Year Type naval gun was the standard surface battery for Japanese submarine cruisers of World War II.
 Most carried single guns, but Junsen type submarines carried two.
 Japanese submarines "I-7" and "I-8" carried an unusual twin mounting capable of elevating to 40° .
 Eleventh year type refers to the horizontal sliding breech block on these guns.
 Breech block design began in 1922 CE, the eleventh year of the "Taishō" period.
 The gun fired a projectile 14 cm in diameter, and the barrel was 40 calibers long (barrel length is 14 cm x 40 = 560 centimeters or 220 inches).
The Paris Gun (German: "Paris-Geschütz / Pariser Kanone" ) was the name given to a type of German long-range siege gun, several of which were used to bombard Paris during World War I.
 They were in service from March to August 1918.
 When the guns were first employed, Parisians believed they had been bombed by a high-altitude Zeppelin, as the sound of neither an aeroplane nor a gun could be heard.
 They were the largest pieces of artillery used during the war by barrel length, and are considered to be superguns.
The Krepost Sveaborg was an Imperial Russian system of land and coastal fortifications constructed around Helsinki during the First World War.
 The purpose of the fortress was to provide a secure naval base for the Russian Baltic fleet and to protect Helsinki and block routes to Saint Petersburg from a possible German invasion.
 Krepost Sveaborg was part of Peter the Great's Naval Fortress, a coastal fortification system protecting access to Saint Petersburg by sea.
 The central part of Krepost Sveaborg was the old fortress of Suomenlinna where the fortress headquarters were located.
 Due to technological advances in artillery the old fortress was no longer capable of providing a sufficient protection, and a new main defensive line was built well beyond the old fortress boundaries.
 New coastal artillery guns built on outlying islands protected Krepost Sveaborg from the sea, while fortified lines constructed around Helsinki were intended to stop any attacks on land.
 The primary coastal guns were 10 in model 1891 guns and 6 in model 1892 Canet guns. Older 11 in model 1877 guns were also used.
 In summer 1917 the fortress had two hundred coastal or anti-landing guns, of which 24 were 10-inch guns in six batteries, 16 were 6-inch Canet guns in four batteries and twelve were 11-inch guns in three batteries.
 The artillery used in land fortifications included older coastal guns, old fixed carriage guns and newer light field guns.
 In March 1917, Krepost Sveaborg had a total of 463 guns, although many of them were obsolescent.
 Krepost Sveaborg was still partly incomplete in 1917 when the February Revolution halted most of the construction work.
 Some further construction work was carried out during the remaining year, but all work halted during the October Revolution.
 Following the Finnish Declaration of Independence, parts of the land fortifications were used in the Finnish Civil War.
 The coastal fortifications were later taken over by Finland to protect Helsinki, while the land fortifications were mostly abandoned and disarmed.
The 1.1"/75 caliber gun was an American anti-aircraft (AA) weapon of World War II, used by the United States Navy.
 The name means that it had a bore diameter of 1.1 in and barrel length of 75 × 1.1 inches = 82.5 in , using the "caliber" nomenclature common to large artillery pieces.
 The gun was designed to replace the M2 Browning and four barrels were required to duplicate the rate of fire.
 The first shipboard installation in 1939 was quickly nicknamed the Chicago Piano, possibly because it was the size of a baby grand piano and looked a little like a baby grand without its lid.
 (Although the reminiscences of the sailors who served with these guns all agree on the nickname, no one seems to know where it originated.)
The 3"/70 Mark 26 Gun was developed to protect United States Warships from kamikaze attacks in World War II, based on the 3"/50 caliber gun.
 The name indicates in US Navy terminology that this piece of naval artillery fires a projectile 3" (7.62 cm) in diameter and has a barrel length of 70 calibers (barrel length = 3" x 70 = 210" or 5.33 meters).

Question: Who ran the company that produced the largest pieces of artillery used during World War I by barrel length?
Answer: Gustav Krupp von Bohlen und Halbach