- 134 - Pacific War - Invasion of Saipan, June 11-18, 1944

Last time we spoke about the fall of Mogaung. General Vinegar Joe’s strategy against Myitkyina had turned into a brutal struggle. Stillwells forces were besieging the town while the Chindits battled for Mogaung, diverting Japanese reinforcements in the process. Despite heavy losses, the Chindits captured Naungkyaiktaw with the help of flamethrowers. Gradually Mogaung fell, but the credit was wrongly attributed to the Chinese while it should have gone to the Chindits. Mytikyina withstood endless attacks and at Biak the Americans repelled numerous Japanese assaults. The 2nd battalion, 162nd regiment tossed over to help, but this further complicated supply issues on the plateau. Progress was deeply hampered by water shortages, difficult jungle terrain and supply roads needing repairs. Lastly the battle for Lone Tree Hill saw absolute mayhem and horror, something the Americans and Japanese would never forget.

This episode is the Invasion of Saipan

Welcome to the Pacific War Podcast Week by Week, I am your dutiful host Craig Watson. But, before we start I want to also remind you this podcast is only made possible through the efforts of Kings and Generals over at Youtube. Perhaps you want to learn more about world war two? Kings and Generals have an assortment of episodes on world war two and much more  so go give them a look over on Youtube. So please subscribe to Kings and Generals over at Youtube and to continue helping us produce this content please check out www.patreon.com/kingsandgenerals. If you are still hungry for some more history related content, over on my channel, the Pacific War Channel you can find a few videos all the way from the Opium Wars of the 1800’s until the end of the Pacific War in 1945. 

 

The use of US fleet and escort carriers during the landings on Hollandia and Aitape had convinced Admiral Toyoda’s staff that the American naval force could be drawn into decisive naval battle off of New Guinea. On June 1st, however, a reconnaissance flight had discovered a major build up of enemy vessels at Majuro, suggesting that a new invasion was just days away. The Imperial General Staff reeled with shock in response to this, not knowing whether the Allied objective was Biak, Palau or Saipan. Aboard Toyoda's flagship Oyodo in Tokyo Bay, the naval staff debated, and the debate degenerated into argument. The truth was that no one had a “feel” for the American strategy except one lone staff intelligence officer, Commander Nakajima Chikataka. He said it had to be Saipan. But his fellow staff members scoffed at this. Even the Americans did not have such power that they could mount an operation the size of the three-pronged New Guinea strike as just a feint, they argued. They  further argued that an enemy airfield at Biak would allow the Allies to bomb the Philippines and Palau with their long-range B-24 Liberators. And the American carriers were in evidence off New Guinea, unlike at Majuro. Thinking that Nakajima must be seeing things, Toyoda thus decided that Biak had to be the place. The Japanese unleashed Operation KON, diverting an enormous sum of their naval and air resources to bolster Biak in response to the perceived allied advance.

 

However, in actuality, Admiral Spruance was gathering the largest Pacific force yet seen at Pearl Harbor, comprising approximately 535 ships, ranging from battleships to tugs, carrying a total of 127,500 personnel of Lt-General Holland Smith’s 5th Amphibious Corps. 

They were going to hit Saipan, Tinian and Guam. Designated “Operation Forager” it was to be the end game of Admiral Nimitz Central thurst into the Pacific. Taking these would see strategic airfields only 1400 miles away from Tokyo in the hands of the allies. From there the US Army Air Force could begin their long wished bombing campaign against the Japanese home islands. For the Japanese, Saipan in particular was considered a “home island”. Japan had seized Saipan during WW1 from the German Colonial Empire and she heavily invested in “Japanizing” the island. The Japanese government had encouraged southern Japanese and Okinawans to colonize Saipan, introducing Japanese language and culture to the indigenous peoples there. It was more than just another Imperial asset, in many ways Saipan had become a home island.

Part of the new operation would include Admiral Mitscher commanding the Fast Carrier Task Force 58 stationed at the Marshalls, along with Vice-Admiral Charles Lockwood overseeing 19 submarines and Rear-Admiral Ralph Christie leading 9 submarines operating across the Pacific and Southeast Asia. Operation Forager entailed Admiral Turner's Task Force capturing Saipan and Tinian sequentially with the 2nd and 4th Marine Divisions, followed by the 3rd Marine Division and the 1st Provisional Marine Brigade attacking Guam. The 27th Division was reserved for Saipan and the 77th Division for Guam. The outcome on Saipan would determine subsequent operations, with the Southern Landing Forces also held in reserve for the Northern Landing Forces until June 25. Lieutenant-General Holland Smith's strategy for the Saipan invasion involved landing four assault regiments simultaneously on four beaches in the Charan Kanoa area. Following three days of continuous air and naval bombardments, Major-General Thomas Watson's 2nd Marine Division's 6th and 8th Marine Regiments were to land north of Afetna Point on the Red and Green Beaches, while Major-General Harry Schmidt's 4th Marine Division's 23rd and 25th Marine Regiments would land south of Afetna Point on the Blue and Yellow Beaches.

Thomas Watson was then going to seize the Charan Kanoa Airstrip, afterwards he would sing northeast towards Mounts Tipo Pale and Tapotchau while Schmidt secured Charan Kanoa village, the Aslito Airfield and the islands southern end before moving north to take part in clearing the remainder of Saipan. Alongside this, Smith planned to dispatch the reserve 2nd and 24th Marine Regiments of Lt Colonel Walter Stuart and Lt Colonel Guy Tannyhill over to Scarlet and Black Beaches in the north to divert enemy attention. Two innovations would be tried for Forager. The 4th Marine Division had recently and optimistically accepted the proposal to employ amphibian tanks inland. This was a large part due to the unit's experiences on low and level Roi-Namur, during the Kwajalein assault. The 2nd Marine Division on the other hand, having fought on rugged Guadalcanal and experienced the limitations of LVTs during the Tarawa assault, were more pessimistic. General Watson convinced General Smith that he would only allow the amphibian tanks to advance inland far enough to clear the immediate beach area and that only the first troop-carrying LVT wave would follow them to discharge their troops beyond the beach. All subsequent waves would discharge troops on the beach and not proceed beyond the Tractor Control Line. The reason for this pessimism was that the Marines expected the terrain to be rougher than some predicted. They feared control would be lost over troops embarked in LVTs, concentrated groups of men would be exposed to fire, and that more amtracs would be lost to enemy fire inland. They were needed to return to the Transfer Control Line on the reef's lip where support troops boated aboard LCVPs would be picked up and run to shore in the amtracs. Furthermore, LVTs are not designed for cross-country movement. They have comparatively narrow tracks and low ground clearance, making it easy for them to "belly-out" on rough ground, rocks, and stumps. Amphibian tanks are poor substitutes for medium tanks for the same reasons, and in addition they have very thin armor and a high profile.

The Marine divisions commenced training for Saipan in March, conducting a significant rehearsal between May 14 and 20 off Maui. With all arrangements in place, Admiral Turner’s invasion fleet was poised to depart Hawaii by late May. The slower LSTs were scheduled to set sail for Eniwetok on May 25, followed by the troop transports departing Hawaii five days later. Turner’s vessels were slated to gather at Eniwetok on June 6, coinciding with the departure of Admiral Mitscher’s carriers from Majuro for the Marianas. Between June 8 and 10, Turner then embarked from Eniwetok in echelons, experiencing a relatively uneventful voyage towards Saipan. Meanwhile, the Japanese expedited the deployment of 31st Army units to the Central Pacific, successfully positioning most of their line units at designated locations by the end of May. Additionally, certain disparate units of the 31st Army underwent reorganization into seven independent mixed brigades and five independent mixed regiments to enhance chain of command and troop cohesion.

 

This, however, did not allow adequate time to prepare inland defenses in multiple lines, especially in the case of the Marianas. The larger elevated islands within the Marianas offered strategic advantages for establishing multi-layered defenses, creating strongholds on key terrain features, and positioning reserves centrally for potential counterattacks. However, the Japanese were unable to fully exploit these opportunities due to various factors. Insufficient troop deployments occurred until less than two months prior to the US assault, leaving limited time for comprehensive inland defense preparations. Many coastal defense and anti-aircraft guns were discovered still packed and alongside incomplete positions, due to a shortage of construction materials for fortified installations. Consequently, the high ground at the island's center remained unprepared for defense, and several beach defenses were unfinished. There was an overestimation of the natural ruggedness of the terrain to impede American advances. Despite this, some coastal defense guns were strategically placed within earlier reinforced concrete structures. While Saipan and Tinian lacked significant artificial underwater or beach obstacles, mines were sporadically utilized on their shores.

The Japanese also suffered from a lack of anti-aircraft ammunition to counter the enemy air superiority. Over on Saipan, Lieutenant-General Saito Yoshitsugu commanded a significant military presence including the 43rd Division, the 47th Independent Mixed Brigade, the 9th Tank Regiment, the 1st Battalion of the 18th Regiment, and various support units totaling 25,500 personnel. Despite its apparent strength, a convoy carrying reinforcements for the 43rd Division was ambushed by two American submarines between June 4 and 6, resulting in the loss of five transports and nearly decimating the 118th Regiment. Saito, overseeing Saipan as commander of the Northern Marianas Army Group, was joined by Admiral Nagumo's Central Pacific Area Fleet headquarters, bolstering defense with an additional 6,200 naval personnel. Additionally, General Obata, stationed at Saipan's army headquarters, delegated authority to his chief of staff, Major-General Igeta Keiji, as he inspected defenses in Palau during the American landings. Saito organized Saipan's defense into five sectors, anticipating landings on the island's west and northwest coasts, Tanapag Harbor, and the north shore of Magicienne Bay. The Japanese strategy relied on tank-infantry counterattacks launched at night from designated positions to repel enemy landings. However, American bombardment of Saipan commenced before Saito's forces could fully fortify their positions. Large numbers of heavy weapons, ranging from 200mm mortars to 5-inch coastal defense guns and literally dozens of searchlights and antiaircraft guns still remained in naval depots or loaded on railroad cars or still packed in cosmoline near partially excavated gun positions. The high ground in the island's center had received little attention in the defensive preparations; and, indeed, beach defenses themselves were in many cases far from complete. In so far as training in defensive warfare is concerned, Japanese forces displayed a marked deficiency; there was little evidence of organization of the ground, the principal airfield (Aslito) was virtually undefended against ground troops, and their counterattack plans were poorly conceived.

On the afternoon of June 11, Mitscher’s Task Force 58, began a relentless three and a half day heavy bombardment against Saipan, Tinian, Guam, Rota, and Pagan. This onslaught, featuring a 225-plane fighter sweep, caught the Japanese off guard in the Marianas and resulted in the destruction of 150 enemy aircraft, securing air superiority for the rest of the campaign. On June 12th and 13th, 216 carrier bombers hit Guam, Saipan, and Tinian, while Admiral Hoover's B-24s started pounding the southern Marianas airfields. You might be raising your eyebrows, the B-24’s belonged to Task Force 57, under Vice-Admiral John Hoover, which was currently formed by the 5th Air Force over on Cape Gloucester and New Guinea; the 7th Air Force and 4th Marine Aircraft Wing on the Marshall and Gilbert Islands; and the 13th Air Force on the Admiralty Islands. Concurrently, two Japanese convoys were intercepted, leading to the sinking of 16 enemy vessels. The first of these, was a formation of 20 ships, fleeing on a northerly course 125 miles west of Pagan Island. They were attacked on the afternoon of the 12th by planes of Rear Admiral William K. Harrill’s Task Group 58.4. Further  south, 135 miles west of Guam, the other convoy of six ships became the target for a special attack mission sent by Rear Admiral Joseph J. Clark, commanding Task Group 58.1. Between the two attacks 12 cargo ships, three submarine chasers, and one patrol-torpedo boat were sunk. Additionally, on June 13th, Mitscher's fast battleships shelled Saipan, though with limited success. The following day, Turner's fire support ships joined Task Force 58 in bombarding Saipan's beaches and installations, effectively neutralizing most of the Japanese coastal defenses and anti-aircraft positions. Despite some damage inflicted on the destroyer Braine and battleship California, Saito's defenses were not completely destroyed, indicating that the preliminary bombardment was not entirely effective. Meanwhile, underwater demolition teams surveyed the landing beaches, clearing them of mines and obstacles and creating gaps in the reefs for the amphibious approach. Smith's reserves staged a demonstration off Tanapag to divert Japanese attention, while carrier groups were dispatched to prevent enemy aircraft staging through the Bonins, successfully attacking Iwo Jima, Chichi-jima, and Haha-jima.

To deter the Japanese from utilizing the Bonins in the north as a staging area for aircraft, two task groups led by Clark's 58.1 and Harrill's 58.4 set sail from Saipan on June 14th for an offensive. This marked the furthest advance into Empire waters by a carrier striking force at that time. Task Groups 58.1 and 58.4 refueled on June 14th and were then dispatched that night toward Chichi and Iwo Jima. Airstrikes on Japanese airfields in those locations commenced the following afternoon despite challenging weather conditions. Despite facing strong resistance from the Japanese, American fighter sweeps and bombing runs resulted in the destruction of 28 out of 37 Zeros engaged, with an additional seven destroyed on the ground, while only two American aircraft were lost. Adverse weather hampered morning strikes on the 16th, but the afternoon sortie of 54 American aircraft encountered Japanese planes on the runway, claiming 63 destroyed, though this wasn't confirmed by Japanese sources. Only two American aircraft were lost due to anti-aircraft fire and operational issues. Despite airborne opposition and unfavorable flying conditions, the mission achieved its objectives, significantly diminishing the Bonins' effectiveness as an aircraft staging area. After the afternoon raid, the two task groups headed south as per Mitscher's orders to position themselves off Saipan by the 18th. This operation proved successful, as around 100 Japanese aircraft that could have intervened in the impending battle were eliminated.

On the morning of June 15, while the landing craft were lowered and began the complex assembly process, the Americans carried the last air and naval preparations on Saipan. At 8:12am, Turner finally gave the landing signal and the amtracs began to approach their assigned beaches under the cover of the LCI gunboats’ rockets. Enemy fire was light until the LVTs reached the coral reef's lip, at which time artillery, mortar, and machine-gun fire increased drastically. Some control craft had drifted slightly to the north and coupled with a stronger than expected current some 2nd Marine Division units landed north of their intended beaches. The UDTs had not experienced this as the sea conditions and tides were different when they went to work the day before. Once over the reef lip some 400yds from shore, the swell made stationkeeping even more problematic. The swell increased through the day, making unloading and transfer difficult as well as capsizing landing craft and LVTs. The 2nd Marine Division had 31 of its 68 amphibian tanks hit or mechanically disabled before reaching the Tractor Control Line ashore. Nonetheless, in 20 minutes, some 8000 assault troops were ashore despite the strong Japanese artillery fire, albeit suffering heavy casualties. On the Red Beaches, Colonel James Riseley’s 2nd and 3rd Battalions encountered stiff resistance from Hill 500 but still managed to secure a shallow beachhead, subsequently repelling a savage counterattack as the reserve 1st Battalion was landing. To the south, as Colonel Clarence Wallace’s 2nd and 3rd Battalions had both come ashore on Green Beach 1, the 2nd would be sent south to seize Afetna Point while the 3rd advanced inland. Afetna Point was important for another reason than just denying the Japanese excellent positions for enfilading the American landing craft. Possession of the point would make Beach Green 3 available for landing of the tanks of both divisions. Because of an open channel off Green 3, LCM’s carrying tanks could proceed directly to the beach without crossing the troublesome reef that fenced all other beaches. Once through the channel the craft could either move straight into Green 3 or fan out to the north or south and put the tanks ashore, wherever it was desired. The same channel could also be used for logistical purposes after tanks were ashore. As a result, the 2nd met strong resistance, progressing slowly and costly against a determined foe while the 1st Battalion was being landed; yet the 3rd managed to push inland against weaker resistance, finally halting about 900 yards from the O-1 Line. In the afternoon, the reserve 1st Battalion, 29th Marines was also landed and employed to fill the gap between Wallace’s battalions. It’s also important to note that the 4th Company, 9th Tank Regiment conducted piecemeal counterattacks on either side of Charan Kanoa with 14 tanks, losing all but three.

Meanwhile, along the Blue Beaches, the 23rd Marines led by Colonel Louis Jones made headway through Charan Kanoa, facing occasional gunfire, and successfully advanced to the O-1 Line. Despite encountering challenging terrain and harassment from Japanese riflemen, their amtracs managed to secure Mount Fina Susu, albeit with significant losses. Upon reaching the O-1 Line, heavy artillery fire pinned down the Americans. Because of the concentrated mortar and artillery fire which had struck his troops throughout the day, the commander of the 23rd Marines, Colonel Jones estimated that the light forces on the O-1 line would be incapable of holding there for the night without being virtually annihilated. In addition, the regimental commander felt that “pulling back would allow our artillery and air to bring fire on the Jap batteries a short distance inland, better contact could be obtained on the right, and the exposed left flank could be better protected.” Dillon’s 2nd Battalion and Cosgrove’s 3rd Battalion were therefore ordered to establish a defense line generally 800 yards west of O-1 for the night. This involved a withdrawal under cover of darkness of the meager forces on O-1.Concerned about the exposed left flank between the 2nd and 4th Divisions, Colonel Jones directed the reserve 1st Battalion to fill the dangerous gap.

Further south, Colonel Merton Batchelder’s 1st Battalion faced fierce resistance from Agingan Point, repelling enemy counterattacks with the aid of air and naval support. Reinforcement from 3rd Battalion units allowed partial clearance of Japanese positions. The 2nd Battalion to the left encountered enemy concentrations but benefited from the heroic actions of the LVTAs, enabling them to advance inland. 

About half the assault Marines of this battalion were carried to a railroad embankment prior to debarkation from LVTs. Until it reached there, the battalion was subjected to frontal small-arms fire from Japanese behind the embankment. There the small arms fire ceased, but mortar and artillery fire continued. From the direction of Nafutan Point came shells which burst overhead, apparently from antiaircraft guns depressed to fire at ground targets. And, as if troubles to the front and flanks were not enough, two enemy mortars began firing on the Marines from positions 500 yards to the rear. Before a request for assistance could be made, friendly planes spotted the mortars, attacked, and silenced them. Much credit for the 2nd Battalion’s success in pushing inland goes to the LVT(A)s of the Army’s 708th Amphibian Tank Battalion, which, according to the Marine battalion commander, Lieutenant Colonel Hudson, took “more than their share of punishment diverted enemy attention from the amphibious tractors carrying troops ... I shall always re- member the excellent support given to my battalion by the Army LVT(A)’s”. Meanwhile, Marine tanks and artillery, under Turner’s command, were successfully brought ashore, although some tanks and howitzers from the 4th Division were lost to fire and reef obstacles. By late afternoon, the bulk of the reserve 2nd and 24th Marines were landed, with the latter sustaining 400 casualties from accidents and artillery fire.  Lieutenant Colonel Alexander A. Vandergrift,  therefore, deployed his battalion and moved it on foot to an assembly area some 700 yards inland from Yellow 1, near a fork in the rail- road tracks. The men had no more than taken entrenching tools in hand when a barrage of well-directed Japanese artillery fire engulfed them. After the day’s casualties were totalled, it was discovered that the unit had suffered heavily, though it had yet to enter the front line fighting: 25 killed, 72 wounded, 39 missing, mostly those lost on board the overturned LVTs. Other battalions had suffered more heavily, but the real significance of these figures lies in the fact that the 3rd Battalion did not arrive on the beach until 5:27pm. However, by nightfall, only the 25th Marines had reached the O-1 Line, constituting less than one-third of the planned beachhead, with casualties exceeding 2000 during the landings.

After half an hour of the Saipan Invasion, Admiral Toyoda announced Operation A-Go proclaiming "The fate of the Empire rests upon this single battle. Every man is expected to do his utmost." The same Nelsonia words used by Admiral Togo at the legendary battle of Tsushima in 1905. He had created that statement taking Nelson’s signal "England expects that every man will do his duty" at the Battle of Trafalgar. Toyoda planned to destroy the American fleet. Admiral Ugaki’s battleships were to rendezvous with Admiral Ozawa’s carriers in the Philippine Sea to attack the American fleet around Saipan. At 6:35pm on June 15th, the submarine Flying Fish reported that a force of Japanese battleships and at least three carriers had passed through the San Bernardino Strait. The submarines were under orders to report sightings before attempting to attack, so Flying Fish waited until nightfall, then surfaced to radio in its report. The sighting report from the submarine was monitored by the Japanese who knew they had been located. About one hour later, submarine Seahorse also sighted a Japanese force 200nm east-southeast of Surigao Strait. The exact composition of this force was unclear, but was thought to be Yamato and Musashi plus escorts. The submarine was not able to send a signal of its sighting until 4:00am on June 16th. Additionally, throughout the 15th, a growing body of signals intelligence indicated that a major IJN fleet action was underway.

 

Receiving this intelligence on the enemy's intentions, Admiral Spruance made the decision to halt the Guam landings, instructed for unloading at Saipan to continue until June 17th only, and tasked Turner with preparing for an imminent decisive battle. However, that's a podcast for next week. General Saito was on the verge of initiating his counterattack. Throughout the night, there were various probes and minor counterattacks that were swiftly repelled. Nonetheless, the 2nd Battalion, 6th Marines faced a major assault at 3am when a Japanese bugler 75 sounded a loud, clear call on the tense night air, and with a waving of flags, loud screams, and a brandishing of swords, the attack was launched. Added to the din were the shouts of the 6th Marines for “flares.” Illumination shells, fired by the three destroyers, Halsey Powell, Coghlan and Monssen of Task Unit 52.17.3 began to burst over the area, clearly revealing the Japanese attackers. Men of Companies F and I opened with accurate, devastating lire. California joined with a tornado of salvos in front of the Marine lines. The Japanese, stripped by the illumination of the advantage afforded by their superior knowledge of the terrain (so helpful in night lighting), dropped before the Marines’ fusillade. As Japanese fell, others replaced them in the determined onslaught. 

At one point in the fighting, it was feared that the enemy had effected a penetration of Company I, along the coastal road. To contain this Japanese prong, Colonel Riseley shifted one company of the 3rd Battalion, 2nd Marines, company L, into the area. The light of morning, however, revealed that no penetration had been made and that Company B had, in effect, formed a secondary line. By 5:45, the Japanese pressure reached a peak; two Marine 37mm guns near the beach were knocked out and their crews forced back. Although the main positions held, a false report reached the 6th Marines’ command post to the effect that Company F’s lines along the beach had been forced back about 50 yards. This erroneous report, probably fostered by the withdrawal of the two 37mm crews and the infiltration of small enemy groups to the regimental command post, had no basis in fact.

Fortunately, five medium tanks arrived in the nick of time to halt the Japanese advance and thwart their assault. With the dawn of June 16th, the battlefield revealed approximately 700 enemy casualties strewn across the terrain. Meanwhile, as the 6th Marines consolidated their position and the remaining 2nd Marines landed, Colonel Wallace’s 2nd Battalion resumed its offensive against Afetna Point, successfully eliminating enemy resistance and bridging the gap between Marine divisions. Further south, General Schmidt led his three regiments towards Fina Susu Ridge in a coordinated advance. Despite the 23rd Marines encountering formidable enemy opposition in the mountains and marshes, the 25th Marines managed to clear Agingan Point and extend beyond the beachhead, while Colonel Franklin Hart’s 24th Marines in the center made significant progress towards the O-1 line despite facing fierce resistance.

Meanwhile,  Spruance opted to withdraw the unnecessary transports in anticipation of the impending naval confrontation. General Smith made the decision to deploy the reserve 27th Division for landing. Consequently, Major-General Ralph Smith's units, excluding the 106th Regiment, commenced landing operations in the afternoon. However, during the night, Saito initiated his second significant counterattack. The Japanese 136th Infantry (two battalions) and 9th Tank Regiments were to counterattack the center of the 2nd Marine Division sector at 17.00hrs. Yokosuka 1st SNLF was to attack the north flank from the Garapan area and “cooperate with the tanks to annihilate the enemy’s front line and advance towards Oreai (Charan Kanoa) Airfield.” Vice Admiral Nagumo, Commander Central Pacific Fleet and 5th Base Force, was ordered to command the attack personally. The units were still disorganized from the previous night's action and the attack was not launched until 03.30hrs. The objective of the Japanese attack was modest enough: the Saipan radio station, a short 400 yards behind the 6th Marines’ lines. This objective, in itself, represented a revision in Saito’s pre-D-Day policy to “destroy the enemy, during the night, at the water’s edge." Seizure of the radio station area would still leave 500—600 yards distance to the water. This resulted in an estimated 44 tanks and 500 infantry attacking the positions of the 1st Battalion, 6th Marines, and 2nd Battalion, 2nd Marines. The attack began at about 3:30, and the brunt struck Lieutenant Colonel Jones’ 1st Battalion, 6th Marines,  and to a lesser extent the 2nd Battalion, 2nd Marines. The tanks advanced in groups of four or five with Japanese soldiers clinging to them. Poor and ineffective tactics reflected the inadequacy of Saito’s order; some tanks cruised about in an aimless fashion, some bogged down in the swampy ground, some made an effort to break through the lines, still others stopped to let off their pugnacious passengers. The Japanese suffered heavy losses, including approximately 24 tanks and 300 men, while inflicting only 97 casualties. By the end of the initial two days, American forces had incurred roughly 3,500 casualties, approximately 20% of the total for the operation. Concurrently, General Obata had instructed the commanders of Guam, Truk, and Tinian to send reinforcements to Saipan via barge, although only two companies managed to land on Rota by June 22nd. On June 17th, the American offensive resumed, yielding significant progress, partly due to artillery support. General Watson expanded the beachhead area nearly twofold, with the 3rd Battalion, 2nd Marines, and 2nd Battalion, 6th Marines advancing northward to within 1000 yards of Garapan. Meanwhile, Colonel Riseley's remaining units secured the base of Mount Tipo Pale along the O-2 Line, and Colonel Wallace's Marines maneuvered around Lake Susupe to reach the O-1 Line. 

To the south, the 25th Marines led by Colonel Batchelder advanced in a column formation, making headway towards Aslito Airfield by approximately 1500 yards. They managed to secure advantageous high ground along the O-2 Line on the northwest perimeter of the airfield. Simultaneously, Colonel Gerard Kelley’s 165th Regiment also moved towards Aslito, making gains of around 1200 yards despite encountering light resistance. By 2:00pm, the 2nd Battalion had moved to the southwest edge of Aslito Airfield, while the 1st Battalion had become involved in a fight for a dominating ridge line extending from the airfield's southwest corner to the vicinity of Cape Obiam. Infantrymen of the 1st Battalion led by Major James H. Mahoney inched slowly up the steep and open slope, so that, by 5:00pm, a toehold had been gained at the crest. At this point, however, the Japanese launched a counterattack and drove the soldiers back off the hill. Reorganizing and reforming the lines at the base of the ridge, the battalion dug in for the night. Amid heavy artillery bombardment, the 24th Marines reached and secured the O-2 Line, consolidating their position on the ridge. In contrast, progress for the 23rd Marines to the south of Lake Susupe’s swamps was minimal as they faced entrenched enemy forces. With the expansion of the beachhead, additional Corps units landed, including General Smith’s command post, advance parties of the Corps artillery, and Colonel Leonard Bishop’s 105th Regiment. During the night, Saito launched another counterattack, deploying the 1st Battalion of the 18th Regiment to stage a counterlanding on the Marine beachhead. However, the intervention of LCI gunboats and Marine artillery thwarted the attempt, driving the enemy back to Tanapag Harbor. Shifting focus to the Battle of Biak, General Fuller’s forces had previously seized Mokmer but now found themselves encircled by Colonel Kuzume’s formidable positions in the East and West Caves. Despite progress in repairing the airdrome, intense Japanese fire prevented its use until the enemy cave strongholds were neutralized.

In contrast, the Japanese had attempted twice to reinforce Biak but failed both times. However, Operation KON drew the Allied forces away from the island, allowing barges to discreetly bring reinforcements from the southwest to Biak without naval protection. As a result, most of the 2nd Battalion, 221st Regiment was successfully transported to the island by June 12, and General Numata was evacuated during this period. Following this success, the 2nd Battalion, 219th Regiment was loaded onto barges in Sorong and transported to Biak via Noemfoor Island, arriving successfully by June 16. Meanwhile, as Colonel Newman’s 186th Regiment secured its positions on June 8, Fuller decided to send the rest of Colonel Haney’s 162nd Regiment to the recently secured Parai Jetty. With the Ibdi Pocket contained, Haney made significant progress toward Mokmer. The next day, Haney continued his advance, successfully connecting with his 2nd Battalion despite heavy mortar fire. Newman faced multiple night counterattacks and was unable to expand his beachhead. On June 10th the 1st Battalion, 186th Infantry, sent two companies to the point on the low ridge where Company B had been halted the previous afternoon. Despite artillery support, the two units could make little progress and were themselves pinned down about 10:30. Japanese rifle and mortar fire was silenced by the 1st Battalion's 60-mm. mortars, but the Japanese continued to pour machine gun fire from a number of bunkers and pillboxes which proved impervious to bazooka and 75-mm. tank fire. The units withdrew while more artillery fire was placed along the low ridge. On the east flank, enemy fire from the East Caves had died down, and the 2nd Battalion, 162nd Infantry, was able to move on eastward. On that same day, as Admiral Toyoda ordered a third attempt for Operation KON, Admiral Ugaki’s battleships were directed to support Admiral Sakonju’s convoy, assembling at Batjan Island on June 11th. The start of the Marianas bombardment on that day forced Toyoda to suspend the operation and prepare for A-Go, ordering the battleships to rejoin Admiral Ozawa’s command and sending the 23rd Air Flotilla to Palau to reinforce Admiral Kakuta’s 1st Air Fleet.

With two regiments now stationed at Mokmer, Fuller decided to resume his offensive by advancing westward towards Borokoe and northward towards the low ridge. The 163rd Regiment was assigned to hold the Ibdi Pocket and the East Caves. On June 11, the assault battalions began moving to the starting point in front of Menoebaboe. Haney's forces faced strong resistance and only reached the starting point by afternoon. The Americans then crossed the starting line, encountering minimal resistance along the coast but significant opposition on the low ridge. As a result, three battalions reached the 1st Phase Line, while Haney's 3rd Battalion couldn't move beyond the starting line. This forced Newman to pause his advance temporarily until Haney cleared enemy positions on the ridge. On June 12, Haney's 2nd and 3rd Battalions advanced on the low ridge. The 3rd Battalion fought doggedly forward during the afternoon, discovering an ever increasing number of Japanese pillboxes, bunkers, and hasty automatic weapons and rifle emplacements of all kinds, manned by 1st Battalion and 5th Company, 222nd Regiment. Dusk found the unit still some 100 yards short of the line of departure and about 1,300 yards east of the 2nd Battalion. The 1st Battalion, taking no part in the action during the day, moved forward to Mokmer Drome from Parai. Due to heavy Japanese resistance, their progress was slow. The next day, the Americans continued their attacks against enemy positions, but they couldn't close the gap between Haney's 2nd and 3rd Battalions. Fuller concluded that his troops were fatigued and that the Japanese had likely received reinforcements, so he requested an additional infantry regiment. General Krueger planned to send the 34th Regiment from Hollandia, scheduled to arrive on June 18. In response to recent setbacks, General Doe ordered the 1st Battalions of the 162nd and 186th Regiments to support the 3rd Battalion on June 14. These battalions positioned themselves on the terrace above the low ridge, facing the main Japanese strongpoint directly.

In response to the enemy's aggressive action, Colonel Kuzume initiated a tank-infantry counterattack with his remaining forces to push back the enemy battalions, inflicting heavy casualties and disrupting the American advance. Despite this, the Americans managed to regroup and establish a continuous line, while the Japanese sustained significant losses and were unable to execute any further major counterattacks for the rest of the battle. Generals Krueger and MacArthur were unhappy with the progress of operations in Biak, which led them to relieve Fuller of his duties as task force commander. Whether General Fuller's relief as commander of the HURRICANE Task Force was entirely justifiable is a question which cannot be answered categorically. At the time of his relief, the task force had seized Mokmer Drome. Patrols sent westward to Borokoe and Sorido Dromes had found no enemy at those two fields, and General Fuller knew they could be occupied with ease. But he had not sent more troops beyond Mokmer Drome because he believed it more important to secure an overland line of communications to that field and to clear the low ridge so that repair work could continue and at least one strip could be put in service. By June 14th it was only a question of time before the West Caves area and the low ridge would be secured. Indeed, General Eichelberger, who took 3.5 days to acquaint himself with the situation at Biak, drew up new attack plans according to which the 162nd and 186th Infantry Regiments were to be employed in the same area and in much the same manner as General Fuller had been using them. General Eichelberger realized, as had General Fuller, that Borokoe and Sorido Dromes would be no safer than Mokmer Drome as long as the Japanese held the low ridge and West Caves positions. But, in the last analysis, the mission of the HURRICANE Task Force, quick seizure and rehabilitation of the Biak fields, had not been accomplished by mid-June. General Eichelberger then took command of Operation Hurricane on June 15. Although the initial plan was to keep Fuller in charge of the 41st Division, he felt unjustly treated and requested to be relieved of this role as well. Consequently, Doe was promoted to command the 41st Division in Fuller's place.

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The invasion of Saipan was seeing tremendous casualties for both the Japanese and Americans. By the end of the initial two days, American forces had incurred roughly 3,500 casualties, approximately 20% of the total for the operation. This island was not going to be a cake walk by any measure, it would be paid for in blood.