'Vengeance' was the US air operation to shoot down the aeroplane carrying Admiral Isoroku Yamamoto, commander of the Combined Fleet (18 April 1943).

To boost Japanese morale in the period immediately following the loss of the island of Guadalcanal in February 1943, Yamamoto decided to make an inspection tour throughout the South Pacific, but on 14 April, the US 'Magic' naval intelligence apparatus intercepted and decrypted reports of the tour. The original message was encoded in the Japanese JN-25D naval cipher, and was picked up by three stations of the 'Magic' system, including Fleet Radio Unit Pacific Fleet. The message contained specific details regarding Yamamoto’s arrival and departure times and locations, as well as the number and types of aircraft which would transport and accompany him on the journey. Yamamoto would be flying from Rabaul to Ballale airfield on Shortland island, near Bougainville island in the Solomon islands group, on 18 April. He and his staff would be flying in two Mitsubishi G4M 'Betty' medium bombers of the 205^th Kokutai, escorted by six Mitsubishi A6M Reisen 'Zero' fighters of the 204^th Kokutai, to a schedule which would see their departure from Rabaul at 06.00 and arrival at Ballale at 08.00, Tokyo time.

Admiral Chester W. Nimitz, commanding the Pacific Ocean Areas, discussed the possibilities with Admiral William F. Halsey, commanding the South Pacific Area, then authorised the mission on 17 April. To avoid detection by radar and Japanese coast-watchers, the mission would entail an over-water flight to the south of the Solomon islands group, a distance of some 430 miles (690 km). This was beyond the range of the Grumman F4F Wildcat and Vought F4U Corsair fighters then available to the US Navy and US Marine Corps squadrons of Guadalcanal’s 'Cactus Air Force'. The mission was thus allocated to the 339^th Fighter Squadron of Lieutenant Colonel George M. McNeese’s 347^th Fighter Group of Major General Nathan F. Twining’s 13^th AAF, whose Lockheed P-38 Lightning fighters, equipped with drop tanks, possessed the range to intercept and engage.

Planning for this mission was begun by XIII Fighter Command’s Lieutenant Colonel Luther S. Moore of the US Marine Corps for Brigadier General Dean C. Strother’s XIII Fighter Command. Moore arranged for each of the designated P-38 aircraft to be fitted with a ship’s compass at the request of Major John W. Mitchell, the 339^th FS’s commanding officer. These fighters each carried the fixed forward-firing armament of one 20-mm cannon and four 0.5-in (12.7-mm) machine guns, and normally carried two 165-US gal (624.5-litre) drop tanks under their wings. For this raid sufficient 300-US gal (1135.5-litre) tanks were delivered from New Guinea to provide each Lightning with one of the larger tanks.

Eighteen P-38 fighters were tasked for the mission. One flight of four was designated as the 'killer' flight while the remainder, which included two spares, would climb to 18,000 ft (5485 m) to act as top cover for the expected reaction by fighters based at Kahili. A flight plan was prepared by the XIII Fighter Command’s operations officer, Major John Condon of the US Marine Corps, but was then discarded in favour of an alternative plan prepared by Mitchell. He calculated an intercept time of 09.35, based on the itinerary, to catch the bombers descending to land over Bougainville, 10 minutes out from Ballale airfield. Mitchell worked backward from that time and drew four precisely calculated legs, with a fifth leg added if Yamamoto took any other than the most direct route. In addition to heading out over the Coral Sea, the fighters of the 339^th FS would wave-hop all the way to Bougainville at altitudes no greater than 50 ft (15 m), maintaining radio silence en route. Although the 339^th FS officially flew the mission, 10 of the 18 pilots were drawn from the 347^th FG’s other two squadrons.

A thorough, detailed briefing included a cover story for the source of the intelligence stating that a coast-watcher had spotted an important high officer boarding an aircraft at Rabaul, but the pilots were aware that their target was Yamamoto.

The specially fitted P-38 fighters lifted off from Guadalcanal’s Fighter Two airstrip beginning at 07.25. Two of the Lightning fighters assigned to the killer flight dropped out of the mission at the start, one with a tyre flattened during take-off and the second when its drop tanks would not feed fuel to the engines.

In Rabaul, despite urgings by local commanders to cancel the trip for fear of ambush, Yamamoto’s aircraft took off as scheduled for the 315-mile (505-km) trip. They climbed to 6,560 ft (2000 m), with their fighter escort behind and 1,640 ft (500 m) higher, split into two V-formations of three machines.

Mitchell’s flight of four led the squadron 'on the deck' with the killer flight, consisting of Captain Thomas G. Lanphier, 1^st Lieutenant Rex T. Barber, and the spares, Lieutenant Besby F. Holmes and Lieutenant Raymond K. Hine, immediately behind, fighting off drowsiness, navigating by flight plan and dead-reckoning. This proved to be the longest fighter interception mission of the war, and was so skilfully executed by Mitchell that the US force arrived at the intercept point just one minute early, at 09.34, just as the ever-punctual Yamamoto’s aeroplane descended into view in a light haze.

Mitchell ordered his pilots to release their drop tanks, turn to the right to parallel the bombers, and begin a full-power climb. Holmes was unable to drop his tanks and turned back out to sea, followed by his wingman, Hine. Mitchell radioed Lanphier and Barber to engage and they turned to climb toward the eight Japanese fighters. The closest escort fighters dropped their own tanks and began to dive toward the pair of P-38 machines. Lanphier immediately turned head-on and climbed toward the escorts, while Barber chased the diving bomber transports. Barber banked steeply to turn in behind the bombers and momentarily lost sight of them, but when he regained contact he was immediately behind one, and began firing into its starboard engine, rear fuselage and tail unit. Barber then hit the port engine of the Japanese aeroplane, which began to trail heavy black smoke, and rolled violently to port, Barber narrowly avoiding a collision. Looking back he saw a column of black smoke and assumed that his victim had crashed into the jungle.

Barber headed toward the coast at tree-top level, searching for the second bomber, not knowing which bomber carried Yamamoto. Barber spotted the second bomber low over the water off Moila Point just as Holmes (whose wing tanks had finally come off) and Hine attacked it. Holmes damaged the G4M’s starboard engine, which began emitting a white vapour trail, then he and Hine flew over the damaged bomber, carrying Yamamoto’s chief-of-staff, Vice Admiral Matome Ugaki, and other members of Yamamoto’s staff. Barber next attacked the stricken bomber, pieces of it flying off and damaging his own aeroplane, and the Japanese bomber crash-landed in the water. Ugaki survived the crash, as did two others, and all were later rescued.

Barber, Holmes and Hine were now attacked by 'Zero' fighters, Barber’s P-38 receiving 140 hits, and Holmes and Barber each claimed a 'Zero' shot down during this mêlée. The top cover briefly engaged reacting 'Zero' fighters without making any kills, and Mitchell observed the column of smoke from Yamamoto’s crashed bomber. The P-38 machines broke off contact and returned to base, with Holmes so short of fuel that he was forced to land in the Russell islands group. Hine’s Lightning was the only US aeroplane missing, and was never found.

As he approached Henderson Field, Lanphier radioed the Guadalcanal fighter director that 'I got Yamamoto', breaching mission security. Immediately on landing, his aeroplane so short off fuel that one engine cut out during landing run, Lanphier again put in a claim for shooting down the bomber, relating that when he turned to engage the 'Zero' escort fighters he shot the wing off one, rolled inverted as he circled back toward the bombers, and saw the lead bomber turning a circle below him. He stated he came out of his turn at a right angle to the circling bomber and fired, blowing off its starboard wing. He stated that he witnessed Barber shoot down another bomber which also crashed in the jungle. Holmes put in a claim for the G4M which crashed into the water, so it was assumed that three bombers had been downed.

The 15 surviving pilots were not 'debriefed' after the mission because this formal interrogation did not exist in the procedures on Guadalcanal at that time, and thus it was never formally established that no one else witnessed Lanphier’s claim. Lanphier initially received credit for the destruction of Yamamoto’s bomber, but the mission’s other pilots were immediately sceptical. Although one of the most expertly executed missions in history, the interception was subsequently marred by controversy over who actually shot down Yamamoto, and by US Navy outrage over unauthorised releases of operational details to the press, including an October 1943 issue of Time magazine, which featured articles on both the engagement and Lanphier. Mitchell had been nominated for the Medal of Honor for the mission, but as a result of the security issues this was downgraded to the Navy Cross, which he and all the pilots of the killer flight were subsequently awarded.

After the war it was found that none of the escorting Japanese fighters was even damaged, much less shot down, and Lanphier was stripped of his claim for the destruction of a 'Zero'. Since other 'Zero' fighters were taking off from nearby Kahili airfield, both Barber and Holmes were allowed their claims during the second combat. Japanese records also confirmed that only two rather than three bombers had been shot down, and the USAAF later awarded 'half kills' to Lanphier and Barber for the destruction of Yamamoto’s aeroplane.

A videotaped interview in 1985 with one of the escorting 'Zero' pilots, Kenji Yanagiya, appeared to corroborate Barber’s claim, but the US Air Force declined to reopen the issue.

The crash site and Yamamoto’s body were found on the next day in the jungle to the north of Buin by a Japanese search and rescue party, led by an Japanese army engineer, Lieutenant Hamasuna. According to Hamasuna, Yamamoto had been thrown clear of the aeroplane’s wreckage, his white-gloved hand grasping the hilt of his samurai sword, still upright in his seat under a tree. Hamasuna said Yamamoto was instantly recognisable, head dipped down as though deep in thought. A post mortem examination of the body disclosed that Yamamoto had received two wounds, one to the back of his left shoulder and one to his left lower jaw that exited above his right eye. Whether or not the admiral initially survived the crash has also been a matter of controversy in Japan.

The ambush and killing of Yamamoto raised morale in the USA and shocked the Japanese, who were officially told about the incident only on 21 May 1943. To conceal the fact that they were reading the Japanese code, the US authorities told US news agencies the cover story originally created for briefing of the 339^th FS’s pilots.

Captain Watanabe and his staff cremated Yamamoto’s remains at Buin, and the ashes were returned to Tokyo aboard the battleship Musashi, the admiral’s last flagship. Yamamoto was given a full state funeral on 3 June 1943, when he received posthumous promotion to the rank of fleet admiral.