'Reno' was a US series of five plans for the advance of the forces of General Douglas MacArthur’s South-West Pacific Area command through the Japanese-occupied Bismarck islands archipelago and to the west along the north coast of New Guinea and the eastern part of the Netherlands East Indies in preparation for an invasion of the Philippine islands group (summer 1942/July 1944).

This was the basic strategic scheme to which MacArthur worked between mid-1942 and mid-1944 with the object of recapturing the Philippine islands as the major stepping stone in his northward advance to the Japanese home islands, a scheme MacArthur and his chief-of-staff, Lieutenant General Richard K. Sutherland, advocated as strategically superior to the alternative 'Granite' advocated by Admiral Chester W. Nimitz’s Pacific Ocean Areas command (an advance to the Mariana islands via the Gilbert and Marshall islands, followed by an offensive to Iwo Jima in the Bonin islands group and then to Okinawa in the Ryukyu islands group) and by Admiral Ernest J. King’s US Navy Operations Staff (an advance to the Mariana islands group via the Gilbert and Marshall island groups, followed by an offensive to Formosa off the coast of mainland China).

The recapture of the Philippine islands group was the primary objective of MacArthur’s strategic planning between the time of his departure from Corregidor island in March 1942 and his highly publicised return to Leyte island in October 1944. From the very beginning of Japan’s expansion to the south from December 1941, the strategic location of the Philippine archipelago had constituted the core of Japan’s the island empire of the 'Southern Resources Area' and inevitably, therefore, the ultimate objective of the South-West Pacific Area command’s overall vision, and after its liberation the main base from which the final assault against the Japanese home islands would be launched.

As the Allied forces advanced to the west along the north coast of New Guinea and through the island groups of the Central Pacific, there developed a dichotomy of strategic thinking among the Allies' planners about the optimum way to bring about the eventual defeat of Japan, but MacArthur never budged from his basic plan of a steady advance along the axis from New Guinea to the Philippine islands group, and thus from Port Moresby to Manila. This plan was conceived as the advance of ground, sea and air forces, fully co-ordinated for the provision of mutual support, along a single axis with the aim of isolating major groupings of Japanese forces which could then be attacked and destroyed at leisure or, at a lower cost to the Allies, slowly starved into surrender. By opting for the route from Australia via New Guinea and the Halmahera islands group to the Philippine islands group, MacArthur ensure the protection of his own forces' lines of communication and supply by pushing his own land-based air cover steadily forward with each advance. His plan was conceived to ensure control of the air and sea during major amphibious operations, and designed to maximise the advantages conferred by his own land-based air power with its inherent tactical advantages.

This remained MacArthur’s fundamental operational concept as he moved his forces from Port Moresby and Milne Bay to Buna and Lae, across the Vitiaz Strait into the Admiralty islands group, forward to Hollandia and the Vogelkop in Dutch New Guinea to reach their final springboard on Morotai island.

The first of the South-West Pacific Area’s overall plans designating the Philippine islands group as its final objective was developed by MacArthur’s planning staff at the conclusion of the Buna and Gona campaign early in 1943. This 'Reno Plan' formed the basis for ensuing operations against the Japanese, and underwent several changes during the course of the Pacific War.

The initial 'Reno I' was based on the premise that the Philippine islands group, lying across the primary maritime routes from Japan to the sources of her vital raw materials and oil in the 'Southern Resources Area' (Netherlands East Indies, Malaya and French Indo-China) was the most important strategic objective for the South-West Pacific Area, for control of the air and naval bases in the Philippine islands group dominated the vital artery of supply to Japan’s war industries. The severance of this artery ensured that Japan’s resources would soon dry up, and her ability to maintain her war-making capability against the advancing Allies would be degraded to the point at which her main bases would become increasingly vulnerable to capture.

The choice of routes to the Philippine islands group was whittled down to an advance along the north coast of New Guinea as this offered the best possible avenue allowing the full co-ordination of the South-West Pacific Area’s air, ground and naval strengths, Extensive use would be made of airborne troops to take certain key bases and allow other to be bypassed. Mindanao was selected as the tactical objective for the initial descent on the Philippine islands group, and the flanks of the Allied advance beyond the western tip of New Guinea were to be safeguarded by the neutralisation of Japanese strength in the Dutch East Indian island of Ambon and in the Palau islands group by Allied air and naval strength.

However, the rapidly changing combat situation of 1943 demanded modification of the basic 'Reno I' plan, and in August 1943 this was replaced by 'Reno II' and in October of the same year by the further modified 'Reno III'.

The basic 'Reno I' plan was thus fleshed in slightly fuller form by 'Reno II' plan, which postulated an orderly progress (under cover of US land-based air power) via New Britain (so that the headquarters and base areas of General Hitoshi Imamura’s 8^th Area Army and Vice Admiral Gunichi Mikawa’s 8^th Fleet could be destroyed), the north coast of New Guinea, the islands of Halmahera, Morotai and Manado in the Dutch East Indies, and thence into Mindanao in the Philippine islands group. 'Reno III' featured the concept of bypassing New Britain (which was to be reduced later, together with New Ireland) in February 1944, then the occupation of the north coast of New Guinea in two phases by October 1944, followed by the capture of the islands of Halmahera and Manado in December 1945, and ending with the invasion of Mindanao in February 1945.

By this time MacArthur’s forces had driven past Finschhafen on the eastern tip of the Huon peninsula of Australian North-East New Guinea and penetrated the Japanese basic defence lines in New Guinea to a depth of more than 300 miles (485 km). The strategy of his advance was sketched briefly in a memorandum to the Department of War in Washington, DC: 'This advance is along a decisive operational axis [which] drives a wedge into the [Japanese defensive] perimeter toward a central core – the Philippines – [which] dominates all aerial and shipping lanes employed by the enemy for his current reinforcement and maintenance program…' The establishment of Allied forces in the Philippine islands group would not only sever Japan’s communications with the islands on which she was dependent for the raw materials and energy supplies to run her war industries, but would also provide an ideal base on which to prepare the final assault on the Japanese home islands.

MacArthur then assessed the options for the approach to the Philippines islands group. He believed that an offensive from the area of the South-East Asia Command would be frontal, pushing the Japanese back through a succession of defence lines which they could readily keep supplied, and concluded that a 'major effort along this line of action is undesirable both tactically and logistically'. An offensive across the Pacific would also have to be delivered against Japanese bastions organised in considerable strategic and operational depth. Such an offensive would have to be supported entirely by carrierborne rather than land-based air power, and would be incapable of effectively cutting the Japanese lines of communication or seriously curtailing Japan’s war-making capabilities.

An offensive from the South-West Pacific Area, MacArthur opined, possessed several advantages which he explained as follows: 'The attack from the Southwest Pacific Area departs from a base that is closest to the objective and advances against the most lightly organized portion of the enemy’s defenses, effecting a decisive penetration. It is the only plan that permits an effective combination of land, sea and air power. The advance can be made by a combination of airborne and seaborne operations, always supported by the full power of land-based aviation and assisted by the fleet operating in the open reaches of the Pacific. A penetration of the defensive perimeter along this line results in by-passing heavily defended areas of great extent that will fall, practically of their own weight, to mopping-up operations with a minimum of loss.'

MacArthur agreed that if the forces were available there would be advantages in delivering offensives along each axis, but nonetheless maintained that the Allies' shortage of means in the initial stages, particularly in amphibious capability, should persuade the Allies to limit their effort to a single offensive delivered with maximum strength: 'To attempt a major effort along each axis would result in weakness everywhere in violation of cardinal principles of war, and would result in failure to reach the vital strategic objective at the earliest possible date, thus prolonging the war.' Thus MacArthur was convinced that the maximum-strength concentration on the single most profitable axis of advance was the best way to ensure early victory.

By March 1944, the forces of the South-West Pacific Area had landed in the Admiralty islands group ('Director', 'Backhander', 'Brewer', 'Appease' and 'Beefsteak') and the forces of Nimitz’s Central Pacific Area had taken both the Gilbert and the Marshall island groups ('Cataract', 'Galvanic', 'Longsuit', 'Flintlock' and 'Catchpole'). This opened the possibility of a pair of parallel strategic offensives by the forces of the South-West Pacific Area and the Central Pacific Area to converge on the Philippine islands group and Formosa. The strategic objectives now expounded in the new 'Reno IV' plan were expanded to include the bypassing of Truk island in the south and the seizure of land, naval and air bases in the southern part of the Philippine islands group (Mindanao and Leyte islands in November 1944 and January 1945 respectively) from which to launch an attack on Luzon island in the northern part of the same island group. Bases in Luzon would in turn be used for the support of subsequent Allied assaults on Formosa and the coast of China.

There were ever accelerating developments in the war against Japan in the course of the spring and summer of 1944 as the Allied advance’s gathered momentum. In the latter part of March, naval task force delivered potent attacks on the Japanese positions on Palau, Yap and Woleai islands, and at the end of April a devastating carrierborne air attack fell on the Japanese base at Truk island. The forces of the South-West Pacific Area meanwhile landed at Aitape ('Persecution') and Hollandia ('Reckless'), and during May moved farther to the west to take Wakde ('Straightline') and Biak island ('Horlicks'). On 15 June, powerful elements of the Central Pacific Area landed on Saipan in the Mariana islands group ('Forager') to secure the land area on which great bases could be constructed for the Boeing B-29 Superfortress long-range heavy bombers which were to blast and burn the heart out of Japan’s industries and cities. Thus the Allied forces were fast taking the operational positions from which to launch a powerful offensive into Japan’s main lines of defence.

Once again, therefore, there re-emerged the strategic question of selecting the best points of attack and the most advantageous axes.

A number of proposals suggested the bypassing of certain previously planned objectives, or even of all objectives other than the Japanese home islands themselves. Other plans advocated the use of long-range bombing from the Mariana islands group to force the Japanese into surrender, and still others considered that bases in China were necessary to accomplish the task of defeating Japan, with landings to be made along the Chinese coast from positions in the Philippine islands group. The suggestion was made that the western part of New Guinea, Halmahera island and the Palau islands group all be bypassed for an immediate blow at the Philippine islands group, another plan advocated the capture of airfields in the southern part of the Philippine islands group and then a direct assault on Formosa, and finally it was proposed that the Philippine islands group should be taken as the base for an assault straight into Kyushu, the southernmost of the four Japanese home islands.

Study suggested that some of these proposals should be removed from contention as entailing too great a degree of risk, with the possibility that failure would delay the conclusion of the war by many months. Other suggestions appeared to be more time-consuming and costly in men and materials than substitute objectives which might be found. The plan to compel Japan to surrender by strategic bombing undoubtedly as its merits, but would clearly have to be supplemented with the territorial conquest of numerous vital areas.

Throughout the period in which these strategic proposals were proffered and examined, MacArthur adhered to his original concept. In view of the overall situation in the summer of 1944, MacArthur continued to believe that the route through Halmahera island and the Palau islands group into the southern part of the Philippine islands group, and thence to Luzon, was the most feasible approach to the Japanese home islands. It permitted an advance which could progress under cover of land-based air power from start to finish, with a minimum of risk and with every assurance of success. This route would also be able to exploit the advantage offered by the availability of a large Filipino guerrilla movement, which was already providing valuable intelligence and awaiting the opportunity to aid in the removal of the Japanese occupying forces from their homeland. Apart from its purely military considerations, moreover, the liberation of the Philippine islands group was a duty whose fulfilment had to be undertaken, as far as MacArthur was concerned, as soon as possible. MacArthur outlined his views in a radio signal to the Department of War a few days after completing the final draft of the 'Reno V' plan: 'In my opinion purely military considerations demand the reoccupation of the Philippines in order to cut the enemy’s communications to the south and to secure a base for our further advance; even if this were not the case and unless military factors demanded another line of action, it would in my opinion be necessary to reoccupy the Philippines. It is American territory, where our unsupported forces were destroyed by the enemy; practically all of the seventeen million Filipinos remain loyal to the United States and are undergoing the greatest privation and suffering because we have not been able to support or succor them; we have a great national obligation to discharge…I feel also that a decision to eliminate the campaign for the relief of the Philippines, even under appreciable military considerations, would cause extremely adverse reactions among the citizens of the United States; the American people, I am sure, would acknowledge the obligation.'

'Reno V' appeared in July 1944, and advocated that US forces should strike from the western end of New Guinea and Morotai against southern Mindanao on 25 October 1944 and Leyte on 15 November 1944, following with large-scale landings in the Lingayen Gulf on 1 April 1945 to start the reconquest of Luzon.

US Army and USAAF planners found much to criticise in 'Reno V', but the scheme formed the basis on which the final invasions of the Philippine islands group was based, though the schedule was advanced as a result of the US Navy’s discovery of the much degraded Japanese air strength in the region.