eHangar.com has the most comprehensive set of aviation art work depicting this (in)famous mission. The pictures available here, painted by a wide range of aviation artists, literally document the mission from beginning to end, and the actual shoot-down from practically every angle. Enjoy!

The Mission
To intercept and shootdown a Japanese aircraft carrying a very special passenger.

The Target
Admiral Isoroko Yamamoto, Japan's most esteemed admiral, Commander in Chief of the Japanese Combined Fleet and architect of the infamous attack on Pearl Harbor.

The Assassination Instruments
Lockheed P-38 Lightnings of the USAAF 339th Fighter Squadron.

It was like searching for a needle in a haystack...to fly without navigational aids over four hundred miles of open sea, never higher than the wave tops, and intercept a flight of enemy aircraft. This was the mission that faced Major John Mitchell, Commanding Officer of the USAAF 339th Fighter Squadron, on April 18th, 1943. It was one of the most remarkable ambushes in aviation history.
Just days earlier, code-breakers of the U.S. Naval Intelligence had intercepted and translated a message indicating that Admiral Yamamoto would fly from Rabaul to an airfield on the southern tip of Bougainville on the morning of April 18, 1943. The popular commander had decided to visit some of his island outposts to bolster Japanese morale in the Pacific. It stated that he would be flying to the island of Bougainville on the 18th. The intercepted message even specified that Yamamoto would be in a bomber (called a Betty by the Americans) and escorted by six fighters (called Zeros by the Americans). It also said the flight would arrive at 0800 hours and then Yamamoto would leave Bougainville at 0840 hours by boat for the Shortland Islands.
The intercepted message was forwarded to Admiral Chester Nimitz (American Commander-in-Chief) who, with the backing of President Roosevelt and Naval Secretary Knox, gave the order to kill this man who was such an important cog in the Japanese military machine. A meeting was held on Guadalcanal led by Admiral Mitscher and it was decided to give the job to Major John Mitchell of the U.S Army 13th Air Force, 339th Squadron. This squadron flew P38 fighter planes, the only planes in the area that had the capability of flying to Bougainville (425 miles away) and back again.
Through careful planning, skillfull flying, and exceptional navigation, they intercepted the Japanese Zero fighters and Mitsubishi G4M1 "Betty"bombers at exactly the right place and time.
Eighteen P-38's took off from the 'Fighter Two' airstrip on Guadacanal, but two aircraft soon developed plane trouble and had to abort. After a 2½-hour, four hundred mile flight just above the waves, Major Mitchell's flight of 16 P-38s spotted the enemy flight exactly where they predicted (and hoped) it would be. With 12 of his fighters acting as high cover to fend off escorting fighters, four pilots designated as the “killer” flight by Mitchell were to destroy the Mitsubishi Betty which would be carrying the Admiral.
Both Bettys were downed by the killer flight, although one of the four P-38s, flown by Lt. Ray Hine, was lost.
It was later discovered that the Admiral was shot through the chest by a single fifty-caliber round, killing him instantly. Just months before, Yamamoto had predicted his own death. The loss was a severe blow to the morale of Japan's military forces.