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The invasions covered here were some of the first US attacks on heavily defended beaches in the Pacific, with pre-prepared fortifications along the shore and strong Japanese garrisons (as the author points out, most earlier attacks had either been on very small islands with limited defences, or much larger islands such as Bougainville or New Guinea, where the Americans were able to pick undefended or lightly defended beaches). The invasion of the Marianas was also seen by the Japanese as a crucial battle, meaning that the IJN was sent into battle, only to suffer a crushing defeat in the battle of the Philippine Sea.
For the Japanese these were thus the first island battles where their doctrine of defending at the water’s edge and launching major counterattacks against any beachhead that got established would be put to the test. As we see here that plan failed badly on Saipan and Guam – fighting on the beaches exposed the Japanese defenders to the full might of the US Navy, while the counterattacks tended to be very costly failures.
After the scene setting introduction we move on to a look at the opposing troops, starting with the US Marines. Even in 1944 the Marines were still filled with volunteers (although some had chosen the Marines after being conscripted). This helped encourage the belief that they were an elite force. The Marine Corps had expanded massively since the outbreak of the Pacific War, and by 1944 contained two full corps as well as an impressive array of air power. The newer V Corps was used on Saipan, which would be its first multi-division attack, while the more experienced III Corps was used on Guam. In both cases the corps commanded a mix of marine and US divisions. The Marine divisions were well equipped units, with integrated artillery, tank, engineer and pioneer battalions.
On the Japanese side the defence of all three islands was built around Ocean or Sea Mobile divisions. These had all been established as normal infantry divisions (in 1904, 1941 and 1943) before being converted into ocean divisions, designed to be moved by sea on self propelled barges. As a result they had very little land transport – perhaps not so important on the smaller islands, but it did slow the movement of supplies. Each division was split into three largely self sufficient regiments, each with its own artillery, engineer and support units. They were pretty well equipped with small arms and artillery, but tended only to have a handful of Type 95 Ha-Go light tanks. Each island also had troops from expeditionary units, formed in China and Manchuria by detached part of existing divisions, but then formed into new Independent Mixed Brigades.
We then move onto a look at the opposing doctrines. On the US side we see how a pre-war doctrine developed with the Japanese in mind as a potential enemy was slowly improved after each attack. The US Navy also improved its shore bombardment capabilities, building fake Japanese defences to practice on. By the time of these attacks destroyers were used close inshore to support individual battalions, while older battleships came closer to the targets than in early attacks, to improve the accuracy of their fire. Special command ships had been built, and the Navy and Ground force commanders shared these ships.
On the Japanese side the doctrine before these attacks was to create a hard shell at every suitable invasion beach, with mobile forces to cover the gaps. The enemy were to be defeated by firepower before landing, or by fierce counterattacks if they got ashore. After this failed on Saipan and Guam the plan was changed, defences were now to be built inland, major counterattacks were limited to the first night to preserve the strength of the garrison, and the plan was to pin down the Americans as long as possible on each island. This new strategy did indeed inflict heavier casualties on the Americans and resulted in longer battles, but it was introduced too late, and could only be attempted on Peleliu, Iwo Jima and Okinawa.
We then move onto the three battles. In each case we get a more detailed examination of the Japanese forces, which were often quite a mixed bag. On Saipan for example there were elements of the 43rd Division (part was on Tinian) and the 47th Independent Mixed Brigade (with part on Pagan). There was also a battalion made up of survivors from US submarine attacks on troop transports, an Independent Mixed Regiment and part of the 9th Tank Regiment. The Navy also provided troops. However many of these units had suffered losses on their way to Saipan. Loses to submarines also slowed down the construction of the island defences. The landings were preceeded by four days of naval and and air attacks, before two marine divisions attacked. This was a large scale attack, with the two divisions attacking side by side, each with two regiments side by side and each regiment with two battalions side by side, for a total of eight battalions in the first wave. However they did have a rather ambitious target – the objective for the first day was high ground one mile inland. As we see this this proved to be over-ambitious, both because of the quality of Japanese resistance close to the beach and because of a swamp that limited progress inland to only two routes. However we see how the Marines were able to get tanks onshore and establish a secure beachhead by the end of the day.
On Guam the landings on 21 July went far more smoothly, against weaker opposition, and the book focuses on the fighting on 26 July, when the Japanese launched a large scale counterattack using as many troops as possible (including the walking wounded). The Japanese commander gave himself two days to plan the attack, which was thus far better organised than many of the earlier ‘banzai’ human wave attacks defeated by the Americans. However the result was similar – as we trace the attacks along the US lines we see most of them failing with heavy cost to the Japanese. There were some short lived successes, with some Japanese troops reaching the command post of the 1/21st Marines, but even there the original front line was restored by 0800 hours. The most famous incident in this attack saw Japanese infiltrators reach the 3rd Marine Division’s hospital area, where they were fought off by wounded marines, corpsmen and doctors before reinforcemens arrived. The problem with this type of attack is revealed by the casualties figures – the US 3rd Marine Division lost 166 dead and 645 wounded while inflicting around 3,500 casualties on the Japanese. This weakened the defences for the rest of the battle.
Peleliu was different. This was the first time the Japanese didn’t expect to defeat an invasion, and instead ordered the defenders to deny it to the Americans for as long as possible. The result was a battle that lasted for over two months. This is the only chapter that focuses on a period of combat – in this case the first week of the invasion. Here we see how the Japanese were able to take advantage of the island’s very rugged coral landscape to create inland defensive lines that were almost entirely invisible until they opened fire. The initial lands faced well organised artillery fire, but not the normal desperate battle at the beach or the immediate counterattack. Instead the Marines were forced into a costly battle of attrition. We follow the marines as they fought for individual ridges and had to overcome very well dug in Japanese bunkers, in a battle where progress was always slow and US casualties high. By the time the 1st Marine Regiment was replaced on 21 September it had suffered 1,749 casualties, or 56%.
We get an interesting conclusion that looks at the strengths of the US Marines, and the initial weaknesses of the Japanese doctrine, while also acknowledging that they learnt from their failures. The costly defence of Peleliu showed that the Japanese army had learnt from its mistakes, but too late to stop the American advance.
Chapters
The Opposing Sides
Saipan
Guam
Peleliu
Analysis
Aftermath
Unit Organizations
Author: Gregg Adams
Edition: Paperback
Pages: 80
Publisher: Osprey
Year: 2024