Operation ‘Forager’ – the US forces move into the Mariana Islands

Black and white photo of a Japanese plane falling from the sky in a blaze of fire, over the sea with a ship on it.Operation ‘Forager’ was the seizure of the northern part of the three largest of the Mariana islands within the overall ‘Granite’ and ‘Granite II’ plans in the period between 15 June and 10 August 1944. During the Pacific and South-West Asian campaigns of 1943 and the first half of 1944, the Allies had completed their seizure of the Solomon islands, captured the Gilbert islands (‘Galvanic’) and Marshall islands (‘Flintlock’ and ‘Catchpole’) and finished their recapture of the Papuan peninsula of New Guinea. In the Pacific this brought the Americans up against the main Japanese defence line, which was based on the Palau, Caroline, Palau and Mariana island groups, which were ex-German possessions occupied by the Japanese since the end of World War I and heavily fortified in the period between the two world wars.

The defence of the Mariana islands was the responsibility of Vice Admiral Chuichi Hara’s 4th Fleet, which was headquartered at Truk. The 5th Base Force had been established on Saipan before the outbreak of World War II, along with the 5th Communications Unit and 5th Defence Force, and these were directly responsible for the defence of the Mariana islands. Just before the war, moreover, the 5th Base Force had also been tasked with planning the seizure of the US island of Guam at the southern end of the Mariana islands. The 5th Base Force was redesignated as the 5th Special Base Force in April 1942, when it had only 1,500 personnel. Only the three largest islands (Saipan, Tinian and Guam, all at the southern end of the chain) played major roles in the war. Minor Japanese installations were located on Rota and Pagan islands.

As the US forces were planning their operation against the Mariana islands, Lieutenant General Hideyoshi Obata’s 31st Army on Truk was made responsible for the Japanese army elements in the Mariana islands, and this headquarters later moved to the Palau islands. While the 4th Fleet had overall responsibility for the area, it had also been decided that once any island was attacked, the senior army officer on that island would assume command of all available forces. A major reinforcement of the Mariana islands was undertaken between February and May 1944, and the comparatively large size of the islands allowed the Japanese to adopt new defensive tactics as, unlike the central Pacific atolls, they were large enough to open the possibility of defence in depth, though advantage of this fact was not always exploited to the full, and also some degree of manoeuvre. The islands were also small enough for all or most of the main landing sites to be defended, which was a situation which did not prevail on the larger islands of the South and South-West Pacific areas. Those islands too had limited the defenders’ ability to manoeuvre because of their size, dense vegetation and rugged terrain.

The Allies embarked on a pair of parallel campaigns to break through in the south-west and to penetrate the Pacific defence line. General Douglas MacArthur’s South-West Pacific Area command therefore advanced through New Guinea and onto Morotai island (‘Tradewind’) in the Halmahera islands of the Japanese-occupied Netherlands East Indies as it advanced toward the Philippine islands. Admiral Chester W. Nimitz’s Central Pacific Area command attacked the Mariana islands. The selection of the Mariana islands as a target was influenced by the introduction of the Boeing B-29 Superfortress heavy bomber, for in American hands the Mariana islands could accommodate the airfields that would provide the air bombardment springboard within B-29 range of Tokyo and other strategic targets in the Japanese home islands.

The Japanese were expecting an attack somewhere on their defensive perimeter, but thought an American onslaught on the Caroline islands, farther south, to be more probable. To reinforce and supply their garrisons they needed both naval and air superiority, so ‘A’ was prepared as a major aircraft carrier offensive for implementation as and when needed by June 1944. The Mariana islands lie some 1,000 miles (1600 km) to the north-west of the Marshall islands, and in World War II were ideally located as a strategic stepping stone for a Pacific Ocean Areas offensive toward the Japanese home islands. As noted above, it was also fully appreciated that these substantial islands would provide adequate bases for the fleet of B-29 bombers to be deployed by the US 20th AAF controlled initially from the continental USA by General Henry H. Arnold. There were already relatively small Japanese airfields on the islands, but the US planners were convinced that three huge air base complexes could swiftly be built to provide a platform from which the US bombers could destroy Japan’s cities and war-making potential, possibly removing the need for US forces to invade the Japanese home islands, which all agreed would be an exceptionally costly undertaking. For these reasons, therefore, the successful implementation of ‘Forager’ was wholly vital to US interests.

Initially the scheme did not secure the approval of all US commanders in the Pacific theatre: MacArthur’s South-West Pacific Area command desired reinforcements for its proposed recapture of the Philippine islands, and Nimitz’s Pacific Ocean Areas command was concerned about the threats posed to the US invasion force by lack of a good harbour in the islands and by Japanese land-based air attack in an operational area beyond the reach of any US land-based aircraft. In January 1944, MacArthur and Nimitz met at Pearl Harbor to agree a joint alternative plan for the B-29 bombers to be diverted to MacArthur’s 5th AAF commanded by Lieutenant General George C. Kenney, and for the naval effort in the central Pacific to be directed at the Caroline and Palau island groups rather than at the Mariana islands. Nimitz agreed with MacArthur that their forces should then combine for the invasion of the Philippine islands, starting with Mindanao island. Reports of the Pearl Harbor conference angered the US Joint Chiefs-of-Staff in Washington, and as a result Admiral Ernest J. King, the chief of naval operations, rebuked Nimitz in a letter which reminded Nimitz that in the ‘Granite’ overall strategic plan the Joint Chiefs-of-Staff had already directed the Pacific Ocean Areas command to work toward an invasion of the Mariana islands as any single drive west across the Pacific farther to the south, as envisaged by Nimitz with MacArthur’s support, would leave the US lines of communication open to a Japanese counterstroke from its northern flank. An often underestimated but nonetheless essential background feature of ‘Forager’, and indeed other parts of the central Pacific offensive, was the US Navy’s system of mobile supply and support ‘bases’ to keep the combat forces operational and fed with all the requirements of modern war. These floating bases (repair ships, supply ships, tenders, tugs, floating docks and salvage vessels etc) were designed to anchor in the lagoon of a large atoll in an area safe from Japanese submarine and land-based air attack. The floating base moved with the fleet it supported, and in the period from 1943 to 1945, this base thus shifted from Majuro atoll in the southern part of Marshall islands, to Eniwetok in the northern part of the same group, and then to Ulithi atoll in the Palau islands.

The whole of the ‘Forager’ campaign presented formidable operational problems, and powerful forces were assembled for the task, which was entrusted to Admiral Raymond A. Spruance’s 5th Fleet. Spruance assembled his command in the lagoon of Eniwetok atoll, and all was prepared for Vice Admiral Richmond K. Turner’s Task Force 51 (Joint Expeditionary Force) to assault the islands with the 127,000 men of Lieutenant General Holland M. Smith’s V Amphibious Corps after the defences had been softened by attacks delivered by the aircraft of Vice Admiral Marc A. Mitscher’s Task Force 58, which destroyed some 200 Japanese aircraft and sank 12 cargo ships. For this wide-ranging sweep, which lasted from 11 to 17 June, TF58 was disposed as Rear Admiral Joseph J. Clark’s Task Group 58.1 with the fleet carriers Hornet and Yorktown, light carriers Belleau Wood and Bataan, heavy cruisers Boston, Baltimore and Canberra, light cruiser Oakland, and destroyers Izard, Charrette, Conner, Bell, Burns, Boyd, Bradford, Brown and Cowell; Rear Admiral Alfred E. Montgomery’s TG58.2 with the fleet carriers Bunker Hill and Wasp, light carriers Monterey and Cabot, light cruisers Santa Fe, Mobile, Biloxi and San Juan, and destroyers Owen, Miller, The Sullivans, Stephen Potter, Tingey, Hickox, Hunt, Lewis Hancock and Marshall; Rear Admiral John Reeves’s TG58.3 with the fleet carriers Enterprise and Lexington, light carriers San Jacinto and Princeton, heavy cruiser Indianapolis (with Spruance on board), light cruisers Reno, Montpelier, Cleveland and Birmingham, and destroyers Clarence K. Branson, Cotten, Dortch, Catling, Healy, Cogswell, Caperton, Ingersoll, Knapp, Anthony, Wadsworth, Terry and Braine; and Rear Admiral William Harrill’s TG58.4 with the fleet carrier Essex, light carriers Langley and Cowpens, heavy cruiser Vincennes, light cruisers San Diego, Houston and Miami, and destroyers Lansdowne, Lardner, McCalla, Lang, Sterett, Wilson, Case, Ellet, Charles Ausburne, Stanly, Dyson, Converse, Spence and Thatcher. Vice Admiral Willis A. Lee’s TG58.7 (the ‘Battle Line’) was distributed initially among the other four task groups, and comprised the battleships Washington, North Carolina, Iowa, New Jersey, Indiana, South Dakota and Alabama, heavy cruisers Wichita, Minneapolis, New Orleans and San Francisco, and destroyers Mugford, Conyngham, Patterson, Bagley, Selfridge, Halford, Guest, Bennett, Fullam, Hudson, Yarnall, Twining, Stockham and Monssen: the Battle Line shelled Saipan on 13 June.

Black and white photo of battleship guns firing, with thick discharge of flame and smokeOn 11 June all four carrier task groups had carried their first fighter attack on all of the Mariana islands, and destroyed 36 Japanese aircraft. TG58.4 attacked a convoy which had just departed Saipan and sank the torpedo boat Ootori, three submarine chasers and 10 merchant ships (30,000 tons). On 12 and 13 June TG58.2, TG58.3 and TG58.4 attacked Saipan and Tinian while TG58.1 attacked Guam. However, on 14 and 15 June there were only individual sorties over the Mariana islands as the ships of TG58.2 and TG58.3 were replenished. Off to the north, TG58.1 and TG58.4 attacked Iwo Jima, Chichi Jima and Haha Jima in the afternoon of 15 June and on 16 June. On the way to the rendezvous with the rest of TF58, TG58.4 attacked the island of Pagan again on 17 June.

The US plan for ‘Forager’ involved two main groups of amphibious forces, namely TF52 and TF53. The former was the Northern Attack Force under Turner’s command, and would deliver onto Saipan (and then Tinian) the 66,800 men of the Northern Troops and Landing Force under Smith’s personal command and comprising Major General Thomas E. Watson’s 2nd Marine Division (2nd, 6th and 8th Marines plus the 10th Marine Artillery) and Major General Harry Schmidt’s 4th Marine Division (23rd, 24th and 25th Marines plus the 14th Marine Artillery), with Major General Ralph C. Smith’s 27th Division (105th, 106th and 165th Infantry) as floating reserve: Ralph Smith was replaced by Major General George W. Griner during the Saipan fighting at the express order of Holland Smith. The combined artillery for the ‘Forager’ operation was the responsibility of the US Army’s XXIV Corps as the III Amphibious Corps’s own artillery had been diverted to support the XXIV Corps for the cancelled operation against Yap.

US intelligence estimated that the defence force available on Saipan to Vice Admiral Chuichi Nagumo’s Central Pacific Area Fleet and Obata’s 31st Army amounted to some 20,000 men, though the actuality was 25,470 soldiers including those of Lieutenant General Yoshitsugo Saito’s 43rd Division (118th, 135th and 135th Regiments), Colonel Yoshiro Oka’s 47th Independent Mixed Brigade (ex-1st Expeditionary Unit) and two infantry battalions shipped in from other islands, plus 6,160 sailors and naval troops including the regimental-size 41st and 55th Base Forces, and the battalion-size Yokosuka 1st Special Naval Landing Force.

The campaign started with the aerial bombing and naval gunfire bombardment of Saipan from 13 June. The naval bombardment force included 15 battleships, and in the course of the bombardment 165,000 shells were fired. As this preliminary programme was pressed forward, the assault force closed on Saipan. Within TF52 were Rear Admiral Jesse B. Oldendorf’s TG52.17 comprising the battleships Tennessee, California, Maryland and Colorado, heavy cruisers Indianapolis (allocated to TF58 until 14 June) and Louisville, light cruisers Birmingham, Montpelier and Cleveland, and destroyers Remey, Wadleigh, NormanScott, Mertz, Robinson, Bagley, Albert W. Grant, HalseyPowell, Coghlan, Monssen, McDermut, McGowan, Melvin, McNair, Yarnall, Twining and Stockham; Rear Admiral Walden L. Ainsworth’s TG52.10 comprising the battleships Pennsylvania, Idaho and NewMexico, heavy cruisers Minneapolis, NewOrleans, SanFrancisco and Wichita, light cruisers Honolulu and StLouis, and destroyers Anthony, Wadsworth, Hudson, Halford, Terry, Braine, Guest, Bennett and Fullam together with two APDs, two DMSs and one AVD; for the provision of air support Rear Admiral Gerald F. Bogan’s TG52.14 comprising the escort carriers FanshawBay, Midway, WhitePlains and KalininBay, and destroyers CassinYoung, Irwin, Ross, Porterfield, Callaghan and Longshaw; and also for the provision of air support Rear Admiral Harold B. Sallada’s TG52.11 comprising the escort carriers KitkunBay, GambierBay, Corregidor and CoralSea, and destroyers Laws, Morrison, Benham, Bullard, Kidd and Chauncey. On 14 June the battleship California and destroyer Braine were damaged off Saipan and Tinian respectively by the fire of shore batteries, while the battleship Tennessee, cruisers Indianapolis and Birmingham, and destroyers Remey and Wadleigh suffered lesser damage from near-misses. On 15 June Tennessee again and the cruiser StLouis were damaged, as were LCI(G)-451 and LCI(G)-726. On 22 June the battleship Maryland was struck and damaged by an air-launched torpedo, LST-119 by shore gunfire and the transport PrinceGeorges by a bomb near-miss.

On 15 June Captain Knowles’s TG52.3 transport group of 13 attack troop transports (APAs), five attack transports (AKs) and one dock landing ship (LSD) landed the 2nd Marine Division on the island’s western side just to the north of Afetna Point, and Captain Loomis’s TG52.4 transport group of 13 APAs, three auxiliary attack transports (AKAs) and three LSDs landed the 4th Marine Division farther to the south near Charan Kanoa. The two landing groups were escorted by the destroyers Newcomb, Bennion, Heywood L. Edwards, Bryant, Prichett, Philip, Cony, Mugford, Selfridge, RalphTalbot, Patterson, Bagley, Phelps, Shaw and Renshaw. Further assault waves arrived on landing ships and boats. In all, TF52 consisted of 551 ships, and a total of 67,451 men were disembarked. Within this overall effort, and supported by a feint landing to the north of Garapan, the landings began at 07.00 on 15 June as a force of more than 300 tracked landing vehicles (LVTs) and numerous landing craft delivered 8,000 marines onto eight beaches between points to the south of Garapan and to the south of Charan Kanoa on the southern end of Saipan’s western coast by about 09.00, with the 2nd and 4th Marine Divisions on the left and right of the beach-head respectively.

Careful Japanese preparation (including the placement of flags in the bay to indicate the range) allowed their artillery to destroy about 20 LVTs, but by nightfall the marines had a beach-head about 6 miles (10 km) wide and 1,100 yards (1000 m) deep. The Japanese counterattacked at night but were driven back with heavy losses. On 17 June units of the 27th Division landed to the right of the 4th Marine Division and advanced on Aslito airfield. Again the Japanese counterattacked at night, but again suffered heavy losses without unduly discomfiting the Americans. On 18 June Saito abandoned the airfield.

Although the invasion had surprised the Japanese, who had been expecting an attack farther to the south, Admiral Soemu Toyoda, commander-in-chief of the Japanese navy, nonetheless saw an opportunity to use the ‘A’ force to attack the US Navy forces around Saipan and on 15 June gave the order to attack. But the resulting Battle of the Philippine Sea was a disaster for the Japanese navy, which lost three aircraft carriers and hundreds of aircraft, effectively removing any opportunity for the reinforcement and resupply of the Japanese garrisons of the Mariana islands.

Without resupply, the defenders of Saipan faced a hopeless situation but determined to fight to the last man. Saito organised his troops into a line anchored on Mt Tapotchau in the defensible mountainous terrain of central Saipan. The nicknames given by the Americans to the features of the battle (such as ‘Hell’s Pocket’, ‘Purple Heart Ridge’ and ‘Death Valley’) indicate the severity of the fighting. The Japanese used the many caves in the volcanic landscape as the basis of strongpoints from which to delay the attackers: the defenders hid during the day and then sortied by night, but the Americans gradually developed tactics for clearing the caves by using flamethrower teams supported by artillery and machine guns.

The US operation was marred by inter-service controversy when the US Marine Corps’ Lieutenant General Holland Smith, unsatisfied with the performance of the 27th Division, relieved its commander, the US Army’s Major General Smith, and replaced him with Major General Griner.

Having pulled back to Marpi Point on the extreme northern tip of the island by 7 July, the Japanese had no further place to which they could retreat. Saito ordered his remaining able-bodied troops, totalling some 3,000 men, forward in a suicide charge, and then killed himself. By the time of the island’s capture on 9 July, Japanese losses were 23,811 dead with 1,780 men taken prisoner, and US losses were 3,426 dead and 13,099 wounded or, according to other sources, 3,126 US dead (out of total casualties of 14,111) and about 30,000 Japanese including Nagumo and Saito, the latter commanding in the absence of Obata who was on an inspection tour in the Palau islands at the time of the US invasion. Within the Japanese total were some 8,000 civilian dead, most of them ethnic Japanese who committed suicide in the last days of the battle, some jumping from ‘Suicide Cliff’ and ‘Banzai Cliff’ despite efforts by US troops to dissuade them.

The crew of the USS SOUTH DAKOTA sit with bowed heads, while Chaplain N. D. Lindner reads the benediction held in honor of fellow shipmates killed in air action off Guam After the battle, Saipan became an important base for further operations in the Mariana islands, and then for the invasion of the Philippine islands in October 1944. Bombers based at Saipan attacked targets in the Philippine islands, the Ryukyu islands and the Japanese home islands. The American forces’ next step was the ‘Stevedore’ descent on Guam from 21 July, and the final stage of ‘Forager’ proper was therefore the assault on Tinian, just to the south of Saipan, which was one of the reasons why the Saipan assault force was used for the Tinian operation. Holland Smith had been elevated to Commanding General, Fleet Marine Force, Pacific Fleet, and command of the V Amphibious Corps had passed to Schmidt, Major General Clifton B. Cates assuming control of the 4th Marine Division.

The Japanese garrison on Tinian amounted to 4,700 soldiers of the 29th Division’s 50th Regiment and 4,110 naval troops and sailors of the 56th Guard Force as well as construction and service troops commanded by Colonel Kaishi Ogata and Captain Goichi Oya respectively under the overall direction of Vice Admiral Kakuji Kakuda, commander of the 1st Air Fleet. It is worth noting that the fighting on Tinian was characterised by the first use of napalm in battle. Of the 120 jettisonable tanks dropped by US warplanes during the operation, 25 contained the napalm mixture and the remainder an oil/petrol mix. Of the entire number only 14 failed, and eight of these were then ignited by strafing runs. Carried by Republic P-47 Thunderbolt fighter-bombers, the ‘fire bombs’ were used mainly to burn away foliage concealing Japanese positions.

Rear Admiral Harry W. Hill’s TF52 moved and landed the relevant formations of Schmidt’s V Amphibious Corps, whose 15,614 men were delivered by elements of TG52.4, LSTs and smaller landing craft. Fire support was provided by most of Oldendorf’s TG52.17 and Ainsworth’s TG52.10, and air support by Bogan’s TG52.14 and Sallada’s TG52.11. In the shelling, the battleship Colorado, destroyer NormanScott and LST-481 were hit and damaged by Japanese coastal artillery. Though the island was secured largely by men of the US Marine Corps, US Army aircraft, artillerymen, amphibian vehicles and engineers helped invaluably toward success of the Tinian operation.

Just 3.5 miles (5.6 km) to the south of Saipan across the Saipan Channel, Tinian saw the landings of the 4th Marine Division on the island’s north-western coast as the 2nd Marine Division feinted toward Tinian town in the south-west of the island before following the 4th Marine Division. The operation was supported, as usual, by a naval bombardment and, in this instance, artillery firing across the Saipan Channel from the southern portion of Saipan. The feint toward Tinian town was successful in diverting defenders from the actual landing site on the north of the island. The Japanese adopted the same stubborn defensive tactics as on Saipan, retreating during the day and attacking at night. The gentler terrain of Tinian allowed the attackers more effective use of tanks and artillery than in the mountains of Saipan, however, and the island was secured in only nine days of fighting as the attacking forces drove south with the 2nd and 4th Marine Divisions on the left and right respectively.

On 31 July the surviving Japanese launched a suicide charge, and the island was declared secure on 1 August. Even so, several hundreds of Japanese troops held out in the jungles for months, and the garrison on Anguilla island off the south-western cape of Tinian, commanded by Lieutenant Kinichi Yamada, held out until the end of the war, surrendering only on 4 September 1945. The US casualties totalled 389 killed and 1,816 wounded, while those of the Japanese were 6,050 killed and 236 taken prisoner. After the fighting had died down, Tinian was developed as an important base for further US operations in the Pacific War. Camps were built for 50,000 troops, and 15,000 Seabees turned the island into the busiest airfield of the war, with six 2,600-yard (2375-m) runways for B-29 bombers to attack targets in the Philippine islands, the Ryukyu islands and the Japanese home islands, the bombers directed at targets in the last generally taking off with incendiary bombs (oil, napalm and white phosphorus) and, in the case of the ‘Silverplate’ and ‘Centerboard’ attacks against Hiroshima and Nagasaki on 6 and 9 August 1945, atomic bombs. Isely Field (ex-Aslito airfield) on Saipan was fully operational by mid-November.

[Photos from Marion Doss]