Pacific War: Fewer islands, more hopping?

[raharris1973]

What's the minimum number of preparatory steps needed to get the US in position to invade the Japanese mainland while destroying as much as possible of the forces that could stiffen the home islands defenses?

In OTL there was a strategic debate between advocates of seizing Luzon or Taiwan as a major stepping stone to Japan in late 1944. Could the allies have been even more economical, and arranged to bypass both the larger islands,and seized Okinawa from launching pads in the Marianas, while simultaneously arranging for having a decisive Leyte Gulf style battle there instead of off Philippine waters? Presumably, audacity and bypassing will make Okinawa riskier, however, there should be more of a surprise advantage and less time for fortification compared to OTL.

Finally, was Okinawa a large enough staging ground for an invasion of the home islands? That is, was there going to be some operational need for a large landmass like Luzon as a place to mass troops where they could still train a bit? Or is Okinawa just fine as an air and naval base to support the landing of troops from as far away as the states and New Guinea and Hawaii and the Marshalls?

[Max Sinister]

This topic isn't my strong side, but I'd be interested in a solution as well.

Yeah, so what are the conditions for successful island-hopping? Could the US have afforded to cut corners? They had superiority in about everything, esp. after Midway.

[oscssw]

Ok guys the key point of when and where to invade was determined by the effective range of aircraft. The end point was always Tokyo; The Sneak Attack of the US fleet at Pearl Harbor saw to that. Even in 1942 it was clear that air power was a strategic necessity for both land and Naval action.

On top of that was the god of war, not Mars but Logistics. Although the USN developped a superb Fleet train forward bases were necessary and served the dual purpose of a place to advance air cover and a place to support the fleet as the USN brought the war to the shores of Nipon. So you needed a secure airbase about every 300 miles ALONG your PIN or route of advance. As good and large as us carriers forces became they were essentially an offensive weapon. You can't place long range Army air Corps bombers like B-24s and B-29s on them or Cargo aircraft like the DC-3/C-47s on them.

WOULD YOU LIKE TO KNOW MORE? (Be forewarned this is more about Logistics than battle.)

Chapter VI-1
Amphibious Doctrine in World War II

www.ibiblio.org/hyperwar/USMC/V/USMC-V-VI-1.html

[miletus12]

You have to understand that the American problem was not getting stuff to where the fighting was in those days.

The problem was establishing air cover to protect the arrival of that material and personnel.  

Expeditionary Airfields in the Pacific, 1941–1945

Published July 19, 2021

By Dr. Corbin Williamson, Air War College

Wild Blue Yonder --

Introduction

In recent years the US military has become increasingly interested in operating aircraft from austere, expeditionary airfields due to concerns about competitor’s abilities to threaten established airfields.1 Expeditionary airfields have also been used in supporting operations against terrorist organizations around the world.2 While the growing interest in creating, maintaining, and operating from such airfields is recent, the US military has an established history of constructing and using such airfields. For example, during World War II, the Allied counteroffensive against Japan required aircraft to operate ever further from established bases in Australia and Hawaii. Sometimes this required engineers to construct airfields hours after Japanese forces had been driven off so that air operations could begin within days. A recent biography of Captain Jerry Yellin has illuminated Yellin’s experience flying P-51 fighters from Iwo Jima less than three weeks after US Marines invaded that island.3 Examining the US Army Air Force’s prewar preparations for expeditionary airfields and wartime operations highlights the challenges and solutions adopted to provide airpower from advanced locations in the Pacific in World War II.

Preparing for War

By the late 1930s, the speed and performance of military aircraft had dramatically increased compared to the aircraft used in World War I. The Army Air Corps recognized that these performance improvements would require airfields to handle these faster, heavier planes. Furthermore, the expanded use of tanks and motorized vehicles in ground operations suggested that future conflict would be highly mobile. Accordingly, the Army Corps of Engineers in June 1940 formed the first dedicated aviation engineer unit, the 21st Engineer Regiment (Aviation). This regiment consisted of three aviation engineer battalions designed for independent operations and capable of independent airfield construction.4 These aviation engineer battalions provided the expeditionary airfield capabilities critical to the Pacific Theater in World War II.

The 21st Engineers gained experience in an unlikely place: Louisiana. In September 1941, the Army held a series of large exercises, later known as the Louisiana Maneuvers. These exercises were designed to test the Army’s readiness for modern, large-scale combat operations.5 During the exercises, the engineers improved runways at sites throughout Louisiana under field operating conditions.6 Engineers also studied reports from the British Army’s operations in France in May and June 1940 that also emphasized the need for mobility.7 As a result, the Army focused on providing aviation engineer battalions with light, mobile equipment that could be moved to new locations relatively easily. This emphasis on lighter equipment later caused issues in airfield engineer operations in the Pacific.8

Even before the United States formally entered World War II, American engineers gained experience constructing expeditionary airfields. In August 1941, the US military began developing air bases on islands in the Pacific between Hawaii and Australia. These airfields on Christmas, Canton, Samoa, Fiji, and New Caledonia were designed to provide an air corridor to the South Pacific that was more secure than the existing corridor, which ran from Hawaii to the Philippines through Wake and Guam and was located dangerously close to Japanese bases.9 This work foreshadowed the growing demand for expeditionary airfield construction capabilities that would heavily impact aviation engineer battalions in the Pacific.

By December 1941, the Corps of Engineers had created 12 aviation engineer battalions, with the 21st Engineers serving as the model. The battalions relied heavily on enlisted personnel with construction or engineering backgrounds and were equipped with more than 140 vehicles and over 200 pieces of construction equipment each. Due to the combination of their personnel expertise and equipment, the battalions proved well-suited to the expeditionary warfare the United States waged in World War II. As a result, the number of aviation engineering battalions exploded from 12 to 51 between December 1941 and December 1942.10

New Guinea

In early December 1941, Japanese forces launched a series of offensives across the Pacific, striking Pearl Harbor, Hawaii, and Malaya. Within months, Japan had occupied much of Southeast Asia and established a defensive perimeter that ran from the Aleutian Islands off Alaska through the Central Pacific and New Guinea. While the Battles of the Coral Sea and Midway checked Japan, the Allied counteroffensive began in earnest in August 1942 when US Marines landed on Guadalcanal in the Solomon Islands. For six months, furious air, sea, and ground battles raged in the Solomons. Each side sought to secure control of Guadalcanal and the critical real estate of Henderson Field, the Allied airfield on Guadalcanal. The struggle for Guadalcanal and Henderson highlighted the importance of establishing and maintaining control of advance airfields in the Pacific theater. This factor continued to shape operations in the coming months.


Figure 1: Allied Command Areas of Responsibility in the Pacific11

By the summer of 1943, Allied ground forces had checked Japanese offensives toward Port Moresby in far southeast New Guinea. They were preparing to assault Japanese positions at Lae and Salamaua on the east coast of New Guinea. However, Allied aircraft were primarily based at airfields around Port Moresby, far from Lae and Salamaua. To support the landings, the Allies needed to establish an airfield close to Lae and Salamaua to provide fighter cover for ground operations. Furthermore, an airfield in this area could support air attacks on the major Japanese base at Wewak on the north coast of New Guinea. Japanese aircraft based at Wewak were sure to contest the attack on Lae and Salamaua. Port Moresby-based bombers could reach Wewak, but escorting fighters could not.


Figure 2: Principal Operations in New Guinea and New Britain, 194312

After a ground reconnaissance of the site behind enemy lines, elements of the 871st Airborne Engineer Aviation Battalion were airlifted in early July to Tsili Tsili, a site just over 40 miles west of Lae. Accompanied by Australian infantry to provide ground security, the engineers brought in airmobile equipment to clear room for an airfield. By late July, a grass runway able to support fighters and transports was operational. The in-person reconnaissance of the area helped the engineering work progress rapidly. Aircraft based at Tsili Tsili supported large, Allied air raids on Wewak in mid-August that destroyed several Japanese aircraft. These raids, escorted by Tsili Tsili-based fighters, helped ensure Allied air superiority for the landings at Lae in September. While the engineers had carved out an operational fighter strip in less than a month, they found that airmobile construction equipment was less capable than their normal bulldozers, tractors, and graders. Breaking down this heavy equipment into air-portable loads proved to be a more effective approach.13

Army engineers often initially cleared a grass landing strip for use by transports and fighters to construct advance airfields. Sometimes prefabricated steel mats, called Marston mats, were laid down to create a runway more durable than a grass strip. It would also be less affected by rain, a common occurrence in the South Pacific. For more permanent airfields, the most common construction material was asphalt, then called bitumen. It was poured on top of a gravel layer, though sometimes gravel alone was used when engineers were pressed for time. Asphalt runways could support heavier aircraft, were easily repaired, and took less time to construct than traditional concrete runways. In addition, runways made of Marston mats could be built faster than asphalt runways, though they were less capable.14


Figure 3, Tsili Tsili Airfield, 11 September 194315

The airfield at Tsili Tsili supported subsequent operations during the assault on Lae. In early September, US Army paratroopers seized the Nadzab airfield northwest of Lae to cut off the Japanese escape route to the northwest. The day after the paratroopers landed, the 871st Engineer Aviation Battalion and Australian engineers flew into Nadzab and began improving the airfield. Four days later, more than 400 cargo landings took place on this rough airstrip flying in supplies and further reinforcements. Ultimately the assault on the Lae-Salamaua supported by Allied aircraft flying from the advance airfields at Tsili Tsili and Nadzab area drove the Japanese from northeast New Guinea.16



Figure 4: C-47 Being Unloaded at Nadzab Airstrip, Six Days After the Paratroop Landing17

The Marianas

By the summer of 1944, Allied forces had made significant progress advancing up the northern New Guinea coast and had launched a drive across the Central Pacific, beginning with the invasion of the Gilbert Islands in November 1943. Landings in the Marshall Islands followed in January and February 1944. The next target for the Central Pacific drive was the Marianas Islands, whose airfields would bring the Japanese home islands within range of B-29 bombers. While bombers based in the Marshall Islands could attack targets in the Marianas, land-based fighters could not reach the Marianas. The plan for the invasion of the Marianas called for US Navy aircraft carriers to provide air cover for the landings until airfields ashore could be constructed and fighters flown in. P-47s were loaded onto two Navy escort carriers to be ferried to the Marianas.


Figure 5: Southern Marianas Islands18

The initial landings in the Marianas took place on the island of Saipan on 15 June 1944, nine days after the Normandy invasion of France in Europe. On the morning of 20 June, Army and Marine troops finished seizing the Japanese airfield at Aslito on Saipan. That afternoon ground echelons of the 19th and 73rd Fighter Squadrons arrived at Aslito. The Navy’s 121st Naval Construction Battalion, Seabees, and the Army’s 804th Aviation Engineering Battalion soon began repairing the airfield. The P-47s of the two fighter squadrons began arriving on 22 June, a week after the initial landings, and flew their first mission that day. Fire from Japanese artillery and air attacks inflicted casualties on the ground crews throughout the rest of June and into early July as Army and Marine units cleared out the rest of the island. Despite these challenges, the squadrons maintained high levels of readiness. The 73rd Fighter Squadron regularly maintained 30 P-47s as operational out of 37 planes assigned. The quick work of the Seabees and an aviation engineer battalion brought land-based fighters into action in short order, which aided ground operations.19

Figure 6: P-47 from 318th Fighter Group Taking Off from USS Manila Bay off Saipan, 23 June 1944 (Figure 3)20

The P-47s of the 19th and 73rd Fighter Squadrons immediately took over the air defense of Saipan from Navy carriers, freeing them for other missions. The Army Air Force fighters also flew strike missions supporting ground operations on Saipan, generally attacking preselected targets while providing some on-call close air support. From 24 June to 9 July, the two squadrons flew 144 sorties over Saipan, flying from austere runways. In addition to flying missions over Saipan, the P-47s attacked targets on other islands in the Marianas. This included Tinian and Guam in preparations for landings on both of those islands in July. The landings on Guam occurred on 21 July, and in the following days, the fighters provided support for ground forces advancing across the island. In addition to strike missions, the fighters served as guides for the landing craft headed for the beaches of Tinian on 24 July using white stripes painted under their wings. During the fighting on Tinian, the P-47s employed an innovative method of directing their airstrikes. A Navy TBF Avenger would lead the P-47s toward the target and then mark the target with a machine gun burst or rocket while describing the target over the radio. This technique foreshadowed the more widely known use of Piper Cub spotting aircraft in the Vietnam War to mark targets for strike aircraft. The operations over the Marianas highlighted the need for close interservice cooperation as Army Air Force fighters relieved Navy carriers and then used Navy strike planes as forward air controllers.21

Leyte

In the months after the invasion of the Marianas, US Navy carrier task forces struck targets in the Philippines. Here they encountered weaker than expected Japanese aerial resistance. As a result, the invasion of Leyte, scheduled for 20 December 1944, was moved up to 20 October, and several preliminary operations were canceled. These initial operations would have established airfields in Southern Mindanao, Yap in the western Caroline Islands, and the Talaud Islands between Celebes and Mindanao. Airfields in these locations would have allowed land-based fighters to cover the invasion of Leyte. However, canceling these operations meant the Leyte invasion force would have to rely on carrier-based aircraft until airfields ashore could be established.22


Figure 7: Japanese-Controlled Areas in the Pacific, Mid-October 194423


Figure 8: The Philippines24

The decision to bring the Leyte invasion forward caused significant logistical problems that delayed the construction and repair of airfields on Leyte when combined with other factors. The Army’s XIV Corps had been slated for the Leyte invasion but was replaced with the XXIV Corps since the XIV Corps was still engaged in combat. Elements of the XXIV Corps were already at sea for the planned Yap landings. They had been loaded assuming that early airfield construction was not a top priority given the reduced Japanese air threat in the Caroline Islands. Furthermore, the acceleration of the Leyte landings meant that some transports with airfield construction material had to sail for Leyte while still bulk loaded. Bulk loading maximized the space available in a transport ship, but for invasions, combat loading was preferred since the equipment was loaded in the order it would be needed for the landings. As a result, critical construction materials were buried below other supplies and took time to extract. Finally, the timetable change reduced the time available for aerial reconnaissance, forcing engineers to rely more on prewar maps to assess the terrain.25







Figure 9: Leyte Airfields, 194426



These problems were exacerbated by events that followed the invasion of Leyte on 20 October 1944. Two areas were priority targets for their airfields: Tacloban in the north and several airstrips to the west of Dulag, though these proved to be in worse condition than Tacloban. The initial landings south of Tacloban were hindered by shallow water that snagged several landing craft. As a result, several landing craft were diverted to land their supplies and equipment near the Tacloban airfield, creating serious congestion on the ground around the strip. Clearing this congestion took time and delayed unloading the heavy construction equipment needed for work on the airfield. Heavy rain also slowed work on the airfield, as did the Japanese naval counterattack that led to the Battle of Leyte Gulf from 23–26 October 1944. Although the US Navy defeated the Japanese, the battle diverted the focus of carrier-based aircraft providing air defense over Leyte. The reduced emphasis on Leyte’s air defense during the battle allowed Japanese airstrikes to get through, which slowed construction work. In addition, kamikaze attacks on the Navy’s escort carriers forced dozens of Navy planes to make emergency landings at Tacloban. Twenty-five of these planes wrecked on landing, and their removal caused further delays. Altogether, logistical problems, weather, and Japanese attacks slowed work on the Leyte airfields.27







Figure 10: Work on Tacloban Airfield Near Completion28







Figure 11: P-38 Landing at Tacloban Airfield on 27 October 194429

After a week, the work of three engineer battalions at Tacloban and three aviation engineer battalions at Dulag began to bear fruit. P-38 fighters from the 85th Fighter Wing flew into Tacloban from Morotai, the nearest airfield, on 27 October and began operations.30 However, the poorer terrain around Dulag meant that those airfields did not become operational until 19 November, almost a month after the invasion. Moreover, the limited capacity of Tacloban combined with an austere air warning system meant Japanese air attacks continued to impede Leyte operations throughout late October and into November. Between 27 October and 31 December 1944 Japanese aircraft flew over 1,000 sorties against Leyte. While American fighters shot down more than 300 enemy planes, the attacks damaged facilities, including runways, sank ships, and killed soldiers. Furthermore, the American aircraft devoted to air defense and air superiority missions reduced the Army Air Forces’ ability to prevent Japanese convoys from bringing troops to Leyte, which prolonged the ground campaign on Leyte.31

Ultimately, by early January, sufficient aircraft were based in Leyte to gain air superiority over the central and southern Philippines. Leyte-based aircraft supported the December landings on Mindoro just south of Luzon and the January 1945 invasion of Luzon itself. In February, the US attacked Iwo Jima and invaded Okinawa to establish positions for the planned invasion of Japan. Fighters based on Iwo Jima and later Okinawa supported B-29 raids launched from the Marianas against the Japanese home islands, which began in November 1944.

Conclusion

Reviewing the US military’s experience constructing, maintaining, and operating aircraft from advance expeditionary airfields in the Pacific Theater in World War II highlights several factors that shaped the role of these airfields in operations. First, purpose-built airmobile construction equipment appeared useful in theory. However, in practice, the reductions in capability required to achieve air mobility were not worth the cost. In New Guinea, Army engineers found that breaking down standard, heavy construction equipment into C-47 transport-sized loads was preferable to using lighter construction equipment that was less capable and required more maintenance in the field. Second, prewar preparations such as learning from the British experience in Europe and creating the initial engineer aviation battalions paid substantial dividends in the war in the Pacific. The engineer aviation battalions also benefited from their ability to attract personnel with construction and engineering backgrounds who did much of the airfield work in 1941 and 1942. Finally, in-person surveys of potential airfield sites proved invaluable. Such surveys or reconnaissance missions helped identify problems that would complicate airfield construction efforts. The absence of such in-person surveys was one of the causes of the delay in deploying significant numbers of land-based fighters to Leyte in October and November 1944. The importance of these factors in World War II suggests they may be worthy of consideration by the US military today. These factors inform and prepare for future conflict in an era of great power competition.

Dr. Corbin Williamson

Dr. Corbin Williamson is Associate Dean of the Air War College, and a naval historian whose new book is The U.S. Navy and Its Cold War Alliances, 1945-1953 (University of Kansas Press, 2020)

Notes

1 The views presented in this article are those of the author alone and do not represent the position of the US Government, the Department of Defense, or the US Air Force.

2 Joseph Trevithick, “USAF Wants Units To Rapidly Build And Fly From New Bases In The Middle Of A Future War,” The Warzone, September 19, 2018, www.thedrive.com/the-war-zone/23682/usaf-wants-units-to-rapidly-build-and-fly-from-new-bases-in-the-middle-of-a-future-war; James Deboer, “Marine Corps F-35Cs Make First Arrested Landings At An Expeditionary Airfield,” The Warzone, December 9, 2020, www.thedrive.com/the-war-zone/38068/marine-corps-f-35cs-make-first-arrested-landings-at-an-expeditionary-airfield.

3 Don Brown, The Last Fighter Pilot: The True Story of the Final Combat Mission of World War II (Washington, D.C.: Regnery Publishing, 2021).

4 Stuart Godfrey, “Engineers with the Army Air Forces,” The Military Engineer 33, no. 193 (November 1941): 488.

5 Richard Ketchum, “Warming up on the sidelines for World War II,” Smithsonian 22, no. 6 (September 1991): 88.

6 Dwight Johns, “Maneuvers Notes of Aviation Engineers,” The Military Engineer 33, no. 193 (November 1941): 495.

7 Godfrey, “Engineers with the Army Air Forces,” 488-490.

8 Hugh Casey, Engineers of the Southwest Pacific, 1941–1945, vol. 6 (Washington, D.C.: Government Printing Office, 1951), 419-420.

9 Grace Hayes, The History of the Joint Chiefs of Staff in World War II: The War Against Japan (Annapolis, MD: Naval Institute Press, 1982), 55.

10 Wesley Craven and James Cate, eds., The Army Air Forces in World War II, vol. 7 (Washington, D.C.: Government Printing Office, 1983), 240–44.

11 Philip Crowl, Campaign in the Marianas (Washington, DC: Government Printing Office, 2011), 5.

12 Hugh Casey, Engineers of the Southwest Pacific, 1941–1945, vol. 1 (Washington, DC: Government Printing Office, 1947), 120.

13 Thomas Griffith, MacArthur’s Airman: General George C. Kenney and the War in the Southwest Pacific (Lawrence, KS: University Press of Kansas, 1998), 124–29; Casey, Engineers of the Southwest Pacific, 6:164–68.

14 Karl Dod, Corps of Engineers: The War Against Japan (Washington, D.C.: Center of Military History, 1987), 218–19; William Craig, Eugene Gallagher, and Xiaoxue Wang, “The use of prefabricated bituminous surfacing geosynthetic in World War II and beyond,” Proceedings of the Institution of Civil Engineers – Ground Improvement 168, no. 2 (May 2015): 96–105. Thanks to Colonel Jonathon Byrnes, USAF for his comments on runway construction methods.

15 342-FH-3A32610-67090AC, Record Group 342, Records of US Air Force Commands, Activities, and Organizations, National Archives and Records Administration.

16 Casey, Engineers of the Southwest Pacific, 6:166; Craven and Cate, eds., The Army Air Forces, 7:280–81; David Dexter, Australia in the War of 1939–1945, series 1, vol. 6 (Canberra: Australian War Memorial, 1961), 357.

17 342-FH-3A32977-67081AC, Record Group 342, Records of US Air Force Commands, Activities, and Organizations, National Archives and Records Administration.

18 Philip Crowl, Campaign in the Marianas (Washington, DC: Government Printing Office, 2011), 25.

19 Dod, The War Against Japan, 498; Bureau of Yards and Docks, Building the Navy’s Bases in World War II: History of the Bureau of Yards and Docks and the Civil Engineer Corps, 1940–1946, vol. 2 (Washington, D.C.: Government Printing Office, 1947), 339–40; Army Air Forces in the Marianas Campaign, Operation Forager, pp. 15, 39, Document 00467751, Air Force Historical Research Agency, Maxwell AFB, Montgomery, AL.

20 342-FH-3A38675-A63748AC, Record Group 342, Records of US Air Force Commands, Activities, and Organizations, National Archives and Records Administration.

21 Army Air Forces in the Marianas Campaign, 23–41.

22 M. Hamlin Cannon, Leyte: The Return to the Philippines (Washington, D.C.: Center of Military History, 1996), 8–9; Casey, Engineers of the Southwest Pacific, 6:273, 283.

23 M. Hamlin Cannon, Leyte: The Return to the Philippines (Washington, DC: Center of Military History, 1996), 47.

24 Wesley Craven and James Cate, eds., The Army Air Forces in World War II, vol. 7 (Washington, DC: Government Printing Office, 1983), 277.

25 Casey, Engineers of the Southwest Pacific, 6:283–99.

26 Wesley Craven and James Cate, eds., The Army Air Forces in World War II, vol. 7 (Washington, DC: Government Printing Office, 1983), 357.

27 Casey, Engineers of the Southwest Pacific, 6:283–99; Wesley Craven and James Cate, eds., The Army Air Forces in World War II, vol. 5 (Washington, D.C.: Government Printing Office, 1983), 368–9.

28 342-FH-3A30531-A55475AC, Record Group 342, Records of US Air Force Commands, Activities, and Organizations, National Archives and Records Administration.

29 342-FH-3A30120-68258AC, Record Group 342, Records of US Air Force Commands, Activities, and Organizations, National Archives and Records Administration.

30 Casey, Engineers of the Southwest Pacific, 6:283–99; Craven and Cate, Army Air Forces in World War II, 5:358, 369–70.

31 Craven and Cate, Army Air Forces in World War II, 5:375.

The effective WWII US fighter radius of action is 500 nautical miles (P-38-P-51), because you have to have 20-25 minutes air combat time to attain air superiority and CAS suppression from the sortie base to the target area. Otherwise, you bring the fleet with you and you use aircraft carriers parked next to the objective for as long as it takes to establish airfields ashore. (2 weeks to a month.)  

That means also, how much footprint do you need to defeat the expected air opposition once you are at the target area and ashore and building those forward air bases?  

The answer obviously is, it depends. The closer you are to metro Japan the more Japanese air opposition you should expect.  Would Iwo Jima be big enough to act as an interdiction shield for the Marianas islands  from the Japanese air threat in their home islands? Yes; it proved to be so.  

Okinawa  is another matter; you are caught in a cross threat axis environment. 





Taiwan, East China and Kyushu are your main air threat axes. You will have quite an air fight, possibly bigger than the one the 8th Air Force is fighting at the time in 1944 from the UK. You can get there and establish your air presence, but you will be fighting from then on. Think Okinawa 2X.    

[Max Sinister]

Thinking about the conditions: You may need a week to take an island. The Seabees need three months to build a new air base there. Also, you need some time to win air supremacy, and have to fight on the seas as well. There might be room for improvement - is there?