March 24th - North East of New Guinea, the Battle of the Solomon Sea
The US cryptographers had not yet decoded enough of the Japanese signals to decide what the aims of the carrier force NE of New Guinea were. The most likely possibilities were either another attempt at an invasion (covered by carriers) while the Allies were occupied with the simultaneous invasion of Java, or a feint. Given the previous Japanese operations, the most likely option was considered to be invasion, and as a result considerable reconnaissance assets were used to try and locate a transport force. In fact, while such an invasion had indeed been the preferred Japanese plan, a shortage of transport ships had made this impossible. Their plan was to use their carriers to draw off forces that might have been used to attack their Java invasion, ideally degrading them in the process, then after Java was secured to invade New Guinea again.
Although the Allies had more search planes available, the need to search for a supposed second force meant that the Japanese were the first to spot their enemy. A search seaplane from one of the cruisers accompanying the carrier force had spotted the USS Lexington on the afternoon of the 23rd. However by the time this had been reported and plotted, it was considered too late (and too far) to make a successful strike that day. Admiral Nagumo therefore ordered any Japanese submarines close enough to intercept the US force to attack, while changing course and speed ready for a dawn attack on the US carriers, Additional search planes would be flown off before first light in order to spot them and lead in the carrier planes.
The US carriers had spotted the Japanese plane on their radar, but the seaplane had manoeuvred cleverly to take advantage of the cloud cover, and the US carriers were unable to vector fighters onto the plane by radar alone (at this stage of the war, US tactical control was still not well practised). The US tactic was to be to send out a wide-ranging patrol before dawn, and be ready to conduct a strike as soon as the Japanese force had been spotted. They were still not certain if the plane that had found them had come from a carrier force or a surface force - seaplanes were known to be carried on the Japanese cruisers, which could be accompanying anything.
Both sides sent off their search planes before dawn. The Japanese were concentrating their effort in the area they expected the US carrier (they still assumed only one carrier was present), while the US search had to cover a wider area (but involved more planes). Nagumo was reluctant to use potential strike planes to supplement the search, and as a result the Japanese did not find the US carriers again until 1000. In the meantime the US planes were conducting their own search, and spotted a single carrier (the Shokaku) at 1030. This was reported as a fleet carrier. The Japanese were operating the Ryuju some distance away from the main carrier group, and this was, at the time, hidden under some rain squalls. The two fleet carriers were operating in open order, and as the spotting plane had to dodge into clouds to evade the Zeroes protecting the force, it is possible both fleet carriers were never seen at the same time. As a result of these successful searches, both sides started to ready their strikes; in addition to the extra half hour of warning, the Japanese were to prove much faster at getting their planes armed and into the air.
The Japanese strike formed up and headed for the US carriers at 1115. It would take them an hour to reach the US carriers. Although the Lexington and Enterprise were operating notionally together, they would in fact conduct two separate strikes, as they had not had a chance to train together. Both strikes were on their way before noon, just as the US radar spotted the wave of Japanese aircraft heading towards them.
The Japanese strike consisted of 18 Zero fighters, 36 dive bombers, and 24 torpedo planes. The radar detection allowed the US carriers to clear their decks and hangar decks of explosive and as much inflammable material as possible, in preparation for the coming attack. 18 Wildcats had been retained for defense, and all of these were in the air by the time the Japanese closed the carriers. The weather was variable, rain squalls making it difficult to keep track of both the incoming planes and the maneuvering carriers, and the Japanese planes (following their earlier reports of only one US carrier being present), missed the Enterprise under one of these squalls. While this was good news for the Enterprise, this meant that the full force of the Japanese attack would fall on the Lexington. The highly experience Japanese planes split up into their attack formations, allowing the US fighters to attack some of them before their protecting Zeroes could get into position. While this was happening the US ships had formed their close defensive formation, allowing them to concentrate their fire on the incoming planes.
The defending fighters managed to shoot down 5 Zeroes and 8 of the torpedo planes (as well as disrupting the torpedo planes attacks), however 12 of the Wildcats were lost in this and the following dogfights. As a result of these action, and the heavy AA gunfire from the mutually-supporting US warships, only one torpedo hit the Lexington. The large carrier absorbed the damage without too much obvious effect, the torpedo damage fortunately forward of her machinery spaces.
Unfortunately concentrating on the torpedo planes meant that the dive bombers had been able to make their attack opposed only by the US AA fire. While the AA suites of the US ships had been increased from some years ago, it was still considered light by RN standards, and only 3 dive bombers were destroyed during the attack. The remaining planes launched their 250kg bombs from near-vertical dives onto the Lexington. While the carriers size had helped her absorb the torpedo damage, her poor maneuverability made it more difficult to evade the bombs. The Lexington was hit by four bombs, and took serious underwater damage from a number of near misses. The planes left the carrier burning fiercely and covered in a huge plume of black smoke.
The cautious Nagumu had been holding the Ryuju's small air group in reserve; his intention had been to use it to finish off any US carrier that had survived his first strike. However even as his orders to send the planes off to attack the US carrier force were being sent, the first of the US planes arrived.
The US carriers had sent out a total of 93 planes - 18 Wildcat fighters, 53 dive bombers and 22 torpedo bombers. Due to their inexperience at conducting multiple carrier strikes, the planes had become separated into three groups. This proved unfortunate for the Ryuju, as if the planes had been on course they would have missed her. But as it was the light carrier was just readying her planes on deck for launch when an alert lookout spotted 18 dive bombers and 22 torpedo planes heading straight for her. The Ryuju only had 6 fighters airborne to stop them, and although the US planes had lost their fighter escort, sheer numbers of attackers had already doomed the carrier. Although her defenders shot down 6 of the torpedo planes and 3 dive bombers for the loss of 2 fighters, the rest of the attack force simply overwhelmed her. Unlike the newer fleet carriers, the Ryuju was not fast enough to steam away from the US aerial torpedoes, especially when they were delivered in a hammer and anvil attack. Hit by three torpedoes, her machinery rooms already flooding, the carrier slowed to a dead stop as the dive bombers swept down onto her. Five minutes later, hit by 3 bombs in addition to the torpedoes, the ship was already on fire and listing heavily. She would sink some 30 minutes later.
Of the remaining two group of US planes - one consisting of 9 Wildcats and 17 dive bombers, the other of 9 Wildcats and 18 dive bombers - the second missed all of the Japanese carriers, having either misunderstood or misapplied the directions. The final group however found the Shokaku and Zuikaku - as well as 18 Zero fighters. Seeing the heavy CAP, the planes decided to concentrate their attacks on the Shokaku. Outnumbered by the Zeroes, this was a very difficult task, not aided by the radical manoeuvring of the ship. As a result only two bombs hit the carrier. One did light damage to her stern, hitting well aft (indeed it almost missed). The other hit her dead centre on her flight deck, penetrating it and exploding on her hangar deck. Fortunately for the carrier nearly all her planes were airborne, as the explosion caused a serious fire and left her unable to operate aircraft. However this carrier class was the only one the Japanese had built with serious hanger deck armour (indeed in this respect they resembled the RN Formidable class), and while it took time to extinguish the fires, the carrier was never in serious danger.
With only one flight deck left to them, not all of the returning Japanese planes were able to fit onto the Zuikaku, and a number of the more seriously damaged planes had to be ditched over the side. Meanwhile Nagumu was trying to decide if there were any US carriers left. Only one had been seen, and that had been left burning and sinking fast, according to reports (this misapprehension was ironically aided by the missed US strike - the planes encountered could, just, have come from one carrier. He had lost a light carrier, and the Shokaku would need repairs before she could again operate aircraft. he had also lost a considerable number of planes and pilots. With the US carrier force presumably eliminated, there was no likelihood of any interference in the Java campaign from the east, and s he decided that he would withdraw north, escorting the damaged Shokaku.
The Americans likewise thought they had defeated their opponents. One carrier was certainly sunk, and a second had been reported as 'burning heavily from multiple bomb hits'. As a result, there seemed no chance that the Japanese could land forces on New Guinea, and there was a badly damaged carrier to get back to Pearl Harbor. The US force therefore split into two parts. The undamaged Enterprise, carrying the aircraft from both carriers, would head back to Pearl, keeping between the likely position of any Japanese force and the damage Lexington. The Lexington, escorted by two cruisers and four destroyers, would hopefully be able to make it back. By late afternoon the worst of her fires were out, and she was able to make 8 knots, increased to 15 by the night.
Sadly for the Lexington, although her engineers had performed a miracle of damage control, she would not make it back home. The Japanese had deployed a line of submarines prior to the fleet actions. They had missed the US force on their way out, as their deployment had not been fast enough, however they were now in position to intercept the Lexington as she withdrew. At 0200 on the 25th, the carrier was hit by two torpedoes, which caused serious flooding and finally put her already damaged machinery out of action for the final time. With no power to fight the flooding, the giant carrier slowly took on an increasing list. It was obvious there was no chance now of getting her back to Pearl, and so her crew was taken off and she was torpedoed by one of her escorting destroyers.