The invasion of Tinian (24 July-1 August 1944) took place three days after the start of the invasion of Guam, and after a week the island had been secured by the Americans (Marianas Campaign).
The island was defended by 9,000 Japanese troops under Admiral Kakuda Kakuji, who was said to be a drunk, and Colonel Ogata Keishi, who took effective command. There was one working airfield at the northern end of the island and two more that had been completed during 1944.
Tinian was well protected by natural barriers. Most of the island was lined by cliffs close to the water line, in places reaching over a hundred feet in height. The gap between the cliffs and the shore was narrow and limited the amount of space available for landing operations. There were gaps in the cliffs to the north-west and north-east, but with poor beaches, and at Tinian Harbor in the south-west. The main part of the island was a limestone plateau, lacking the mountains of Saipan or Guam.
The task force reached the invasion area a day early, and so on 11 June Mitscher launched a fighter sweep that caught the Japanese by surprise and destroyed at least 150 aircraft across the islands. Three more days of air attack followed, hitting Saipan and Tinian. The naval bombardment began on 13 June, when seven fast battleships and eleven destroyers were detached under the command of Admiral William A. Lee Jr. This force bombarded Tinian and Saipan between 1040 and 1725, probably with little impact. The main bombardment force - seven old battleships, eleven cruisers and twenty-six destroyers, under Rear Admiral Jesse B. Oldendorf, arrived on 14 June. These ships had far more training and experience of shore bombardment, and were also allowed closer to shore, and they were thus more effective than the fast battleships. Many anti-aircraft guns were destroyed, but the fixed fortifications mainly survived intact.
The invasion was carried out by the 5th Amphibious Corps, the same force that had invaded Saipan. General Holland Smith, who had commanded the corps at Saipan had been promoted to Commander of the General Fleet Marine Force Pacific, and been replaced by General Schmidt, one of his divisional commanders. Two Marine divisions were involved the 2nd Marines under General Watson and the 4th Marines under General Clifton B. Cates.
The Japanese defences were concentrated at the southern end of the island, ready to defend the beaches around Tinian Town. The Americans were well aware of this, and decided to concentrate their efforts in the north-west. There were two narrow beaches in that area, and a close investigation on 10-11 June suggested that they were lightly defended, and just about large enough to support the landings.
The Americans attacked at two points on 24 July. The main attack came to the north-west, where the 4th Marine Division landed. A second, diversionary attack, was made by part of the 2nd Marine Division near Tinian town on the south-west coast. The diversionary attack involved a full naval bombardment, and even saw troops from the 2nd Marines climb down into their landing craft. The Japanese replied with fire from three hidden 6in guns, but these were soon suppressed.
The main landing was supported by thirteen batteries of US artillery firing from nearby Saipan, and another sizable naval bombardment, with two battleships, two destroyers, one cruiser and thirty gunboats bombarding the beaches and three cruisers and four destroyers fighting on the nearby heights. The landings themselves went fairly well. On beach White 1 there was some hand to hand fighting as the Japanese defenders were eliminated. On White 2 two blockhouses had survived the bombardment, but they were soon taken out from the rear. Three LVTs and a jeep were destroyed by an unsuspected minefield, but these were only minor setbacks, and by the end of the day 15,000 US troops were already ashore and the beach head was a mile deep and a mile and a half wide. The Japanese had already lost the battle for Tinian.
Ogata's response was entirely typical - he organised an immediate counterattack to be carried out that night. He committed most of his mobile troops to this attack, and was able to attack all parts of the US beachhead. Like most banzai attacks of the war, this was a costly failure for the Japanese. The US lines held, and the Japanese lost over 1,200 dead to no effect.
On 25 July the rest of the 2nd Marine Division (General Watson) landed on the main beaches. The 2nd Marines cleared the northern end of the island, and the two divisions then pushed south, with the 2nd Marines in the east and the 4th Marines in the west. They used an 'elbowing' technique, with each division attacking in turn, supported by almost all of the artillery. Ogata decided to pull back to an escarpment that ran across the southern end of the island and make his last stand there. The Americans prepared for this final battle with a massive naval and aerial bombardment, in which 684 tons of ordnance were fired at the defenders, as well as a heavy artillery bombardment. The attack began on 31 July, and by late afternoon the Marines were at the top of the escarpment. That night the Japanese briefly cut a road that led to the Marine foothold, and just before dawn launched a final banzai attack with 600 men, but both efforts failed. On 1 August the Americans were able to advance to the southern end of the island, and General Schmidt declared the island to be secure. This was a bit premature, as scattered groups of Japanese troops were still hiding in a series of coastal caves, and launched a number of troublesome attacks. However the main fighting was over.
The Americans suffered 394 dead and 1,961 wounded during the battle, while most of the 9,000 Japanese troops were killed. Around 9,000 civilians surrendered on Tinian, although there were some mass suicides, just as on Saipan. The battle of Tinian was one of the most successful US amphibious landings of the Pacific War, and the island was conquered in a single week. In contrast the battle of Guam, which began a few days earlier, lasted into mid-August.