The Role of Saipan in the Pacific War

The island of Saipan, near the center of the island chain known as the Marianas, became a primary objective for both Japan and the United States in 1944. For Japan, it was one of many islands that formed a protective ring around its home islands. For the United States, Saipan’s geographic location not only recommended it as a target in its own right, but as the first of several that needed to fall in a particular sequence. For both, the battle at Saipan altered the realities of the war and their perceptions of their enemy. The tiny island of Saipan played a crucial role in the Pacific War.

Saipan, along with the other islands of the Marianas, had been held by the Japanese under international mandate since 1919. Several of the islands, including Saipan, produced sugar cane, and were well-populated; Saipan differed from the others in that the bulk of its population was ethnically Japanese. As such, it is natural that the Japanese would wish to defend it, but in 1944 it assumed an importance well beyond that consideration.

The Doolittle Raid of 1942 had shown the Japanese how vulnerable their home islands were to an American air attack. Subsequent fighting had failed to cripple the American fleet; on the contrary, it was the Imperial Japanese Navy (IJN) that had been battered, and it became necessary to husband the naval assets that remained if the IJN were to continue to protect Japan itself. Meanwhile, far-flung outposts in the Pacific suffered as a result. The American strategy of island-hopping was having the desired effect, with the best-prepared Japanese bastions being avoided and weaker targets being seized instead; this, in turn, weakened or neutralized the stronger bastions, which no longer enjoyed supply connections and easy communication with superiors. By the beginning of 1944, the Japanese Empire in the Pacific was shrinking rapidly.

In response, Tojo drew the Marianas into a line of islands extending northeast from the Palaus that must be defended at all costs. With this line in Japanese hands, heavy bombers, which were necessarily land-based, could not reach Japan itself, and an extensive network of airbases among these islands would hinder any effort to project a carrier force to a striking distance from Japan. As for the islands themselves, it was the Palaus which seemed the most strategic target, because the capture of the Palaus would open the prospect of an invasion of the Philippines; in such a contingency, however, the airfields of the Marianas would provide much-needed support for the Japanese defenders in the Palaus. Indeed, a direct attack on the Palau Islands without clearing the Marianas first was the only scenario in which the Japanese could hope to meet the Americans with anything like parity in air power.

For their part, American planners were well aware of these considerations, and they added several of their own. Certainly, General MacArthur was pressing for the liberation of the Philippines, and to accomplish that, it made sense to sweep Japanese air power from the Marianas. At the same time, other voices argued for a more northerly attack route, pointing toward Formosa and Okinawa; in this scenario, too, the Marianas would serve as an invaluable staging point. Control of the Marianas would also cut off the Japanese forces that remained at Truk, while the effort to capture them would draw out the IJN and allow for the possibility of a decisive naval battle. From the Marianas, Japanese shipping and air movement between the home islands and their major holdings could be harassed. And finally, the Americans awaited the delivery of the new B-29 Superfortress heavy bomber, and that bomber could attack Japan itself from the Marianas. Once the Marshall Islands had been taken, the Marianas were the next priority.

In keeping with American strategy, not all of the islands needed to be taken, but in this case, the southerly islands of Saipan, Tinian and Guam were necessary, and they were the largest and best-defended islands in the group. Around 60,000 Japanese soldiers defended the Marianas, mostly in the south; over half of them were on Saipan alone. Also, the air bases were concentrated in the south, and it was these that needed to be cleared in order to facilitate the attack on the Philippines. The northern islands could be left for the moment, but for a variety of reasons, the most heavily-defended island, Saipan, needed to be the first target.

In the first place, Saipan was the northernmost of the islands to be attacked, and lay near the center of the chain. If Saipan were secured first, it would become substantially easier to capture Guam and Tinian. Indeed, Saipan could serve as a staging area for the attack on Tinian, while the capture of Saipan would at least deprive the defenders on Guam of any additional air support. Moreover, Saipan was the local command center, and it would remain the most difficult target in the series, regardless of the order in which they were captured; attacks on Tinian or Guam would be substantially more difficult if Saipan were still in Japanese hands, however, and so it made sense in this case to attack the most difficult target first.

Saipan, like Guam, had a mixed terrain that included rocky heights and numerous caves. American planners had no illusions about the difficulty of the invasion. Saipan also featured a harbor, Tanapag, on its western side, just north of Garapan; most of the western side of the island was protected by reefs. Aslito Airfield was at the far south of the island, while in the north, at Marpi Point, was a serviceable airstrip. The Japanese were in the process of building up their fortifications, and they might have been able to fortify the island much more if not for American submarine efforts, which sank transport vessels bound for Saipan.

The attack began with a naval bombardment and air assault that proved only a partial success. Japanese air forces were devastated, and some of the coastal fortifications were reduced, but preliminary bombardment had done little to weaken Japanese ground troops. Holes were blasted in the reefs to permit landing craft to deliver Marines to the beaches on the southwest end of the island. The invasion accomplished another of its goals when it forced the Japanese to send its Mobile Fleet to try to repel the American Navy. The resulting Battle of the Philippine Sea failed to destroy the Japanese fleet itself, but it negated the Japanese carriers by destroying nearly all of their aircraft. With the Mobile Fleet repulsed, it fell to American ground troops, both Marines and Army, to capture Saipan. It was a long and difficult battle, ending only on July 9, three and a half weeks after the original landing.

Among the horrors of the fighting was the self-destructive impulse shown by many Japanese civilians on the island. The suicidal defense of Japanese soldiers was not new, although it was somewhat more robust on Saipan than on many of the islands captured previously, but this offered Americans the first look at how Japanese civilians might behave in response to an American attack. It was a sobering lesson.

In objective terms, the fall of Saipan gave the Americans their forward base for attacking Japan and its supply lines. It prompted the resignation of Tojo and the transformation of the Japanese war effort into one of staving off defeat for as long as possible. It permitted attacks on the Palau Islands and the Philippines, as well as attacks further north, including the bombing of the Japanese home islands. At the same time, it intensified propaganda on both sides. The Japanese lauded the heroism of the suicidal defenders and the equally suicidal civilians, urging other soldiers and, eventually, other civilians to behave in the same way. The Japanese government thought that by escalating the cost of defeat, it could undermine the American will to achieve victory. It hoped to make a negotiated settlement the only palatable alternative. In this, the measure failed grievously. On the contrary, it hardened American resolve. Faced with the prospect of a foe that would fight to the bitter end regardless of the circumstances, the Americans were compelled to kill as many as possible, as efficiently as possible. American expectations of what fighting in Japan might be like were certainly bolstered by Iwo Jima and Okinawa in 1945, but Saipan in 1944 gave the first taste of the intensity that the Americans could anticipate. In this way, Saipan represents a key moment between the Doolittle Raid in 1942 and Hiroshima in 1945.



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