question: What Japanese unit was commanded by the admiral targeted by Operation Vengeance?
answer: the Combined Fleet
context: Title: Japanese naval codes
  Passage: The vulnerability of Japanese naval codes and ciphers was crucial to the conduct of World War II, and had an important influence on foreign relations between Japan and the west in the years leading up to the war as well.  Every Japanese code was eventually broken, and the intelligence gathered made possible such operations as the victorious American ambush of the Japanese Navy at Midway (JN-25b) and the shooting down of Isoroku Yamamoto in Operation Vengeance.
  Title: I Scouting Group
  Passage: The I Scouting Group was a special reconnaissance unit within the German Kaiserliche Marine.  The unit was famously commanded by Admiral Franz von Hipper during World War I.  The I Scouting Group was one of the most active formations in the High Seas Fleet during the war; the unit took part in every major fleet operation in the North Sea, including the battles of Dogger Bank and Jutland.  The unit also saw limited action in the Baltic Sea, including the Battle of the Gulf of Riga.
  Title: John W. Mitchell (United States Air Force)
  Passage: John William Mitchell (14 July 1915 – 15 November 1995) was an officer of the United States Air Force, a flying ace and the leader of Operation Vengeance, the mission to shoot down Admiral Isoroku Yamamoto.  He served in World War II and the Korean War.
  Title: Ken (unit)
  Passage: The ken (間 ) is a traditional Japanese unit of length, equal to six Japanese feet ("shaku").  The exact value has varied over time and location but has generally been a little shorter than 2 m .  It is now standardized as 1 / meter .
  Title: Shaku (unit)
  Passage: The (shaku ) or Japanese foot is a Japanese unit of length derived (but varying) from the Chinese "chi", originally based upon the distance measured by a human hand from the tip of the thumb to the tip of the forefinger (compare Span).  Traditionally, the length varied by location or use, but it is now standardized as / meters (30.3 cm ).
  Title: Isoroku Yamamoto
  Passage: Isoroku Yamamoto (山本 五十六 , Yamamoto Isoroku , April 4, 1884 – April 18, 1943) was a Japanese Marshal Admiral of the Navy and the commander-in-chief of the Combined Fleet during World War II until his death.
  Title: Warhammer 40,000: Storm of Vengeance
  Passage: Warhammer 40,000: Storm of Vengeance is a real-time strategy video game developed and published by Eutechnyx.  It was released for Microsoft Windows, Android and iOS.  "Warhammer 40,000: Storm of Vengeance" was set in the "Warhammer 40,000" universe, it follows the Dark Angels, commanded by Grand Master Belial, and the Bad Moons, commanded by Ork Warlord Ghazghkull Thraka on the planet Piscina IV.  "Warhammer 40,000: Storm of Vengeance" was released on; 3 April 2014 (Steam), 23 April 2014 (Google Play) and 1 May 2014 (iOS).
  Title: Operation Flintlock (World War II)
  Passage: Operation Flintlock was the campaign against the Japanese in the Marshall Islands in the Pacific theatre of World War II, from 31 January to 4 February 1944.  The operation involved the invasions of Kwajalein, Eniwetok, and Majuro atolls.  Admiral Nimitz, Commander of the U. S. Pacific Fleet, chose two islands in Kwajalein Atoll, Roi-Namur Island and Kwajalein Island, as primary targets in the U. S. invasion of the Marshall Islands.   Kwajalein Atoll contained communication and weather observation units and two Japanese airstrips on Roi-Namur and Kwajalein Islands, a seaplane base situated at Ebeye Island, a submarine base at Roi-Namur Island, and other Japanese installations scattered on various islands throughout Kwajalein atoll.   Kwajalein atoll, particularly Roi-Namur and Kwajalein Islands, were subjected to heavy bombardment.  This attack also sank a large number of Japanese ships in Kwajalein Lagoon.  Bitter fighting between Japanese forces and the U. S. 4th Marine Division on Roi-Namur, and the U. S. 7th Infantry Division on Kwajalein, resulted in a U. S. victory on 4 February 1944.  The attack of the Japanese in the Marshall Islands was the first US attack, and capture, of Japanese territory, since the land was held by Japan before the start of World War II.  The capture of Kwajalein Atoll during Operation Flintlock provided American forces with a base of operations that assured the recapture of the Philippines and eventually the fall of Japan.
  Title: Koku
  Passage: The koku (石) is a Japanese unit of volume, equal to ten cubic "shaku".  In this definition, 3.5937 "koku" equal one cubic metre, i.e. 1 "koku" is about 278.3 litres.  The "koku" was originally defined as a quantity of rice, enough rice to feed one person for one year (one "masu" is enough rice to feed a person for one day).  A "koku" of rice weighs about 150 kilograms (330 pounds).
  Title: Operation Vengeance
  Passage: Operation "Vengeance" was the American military operation to kill Admiral Isoroku Yamamoto of the Imperial Japanese Navy on April 18, 1943, during the Solomon Islands campaign in the Pacific Theater of World War II.  Isoroku Yamamoto, commander of the Combined Fleet of the Imperial Japanese Navy, was killed on Bougainville Island when his transport bomber aircraft was shot down by United States Army Air Forces fighter aircraft operating from Kukum Field on Guadalcanal.
citations: Isoroku Yamamoto John W. Mitchell (United States Air Force)