'Rubber' was a US unrealised joint army and navy plan to land from the sea in the north-western part of neutral Brazil to secure an area for the construction of major air bases for anti-submarine and transport purposes (December 1941/February 1942).

The scheme resulted from US concerns that Brazil would enter the war on the side of the Axis, or would at least act in a manner sympathetic to the Axis.

Brazil occupies a strategic location insofar as far as any crossing of the South Atlantic is concerned, for the north-eastern tip of Brazil is one end of the shortest crossing to French West Africa and Sierra Leone. In 1939, as part of 'War Plan Rainbow', the USA decided that north-eastern Brazil would be secured and made available as a staging point for transatlantic travel to Africa and onwards into Europe and the Middle East, and yet further into the Far East and China in the event that a Japanese opportunistic advance into the Pacific might make the shorter crossing to East Asia unavailable.

After the USA had entered the war in December 1941, it was believed in Washington that, at best, the security of north-eastern Brazil could not be guaranteed or, at worst, that the area and possibly the entire country might side with the Axis powers. The reasoning behind this US fear was complicated, but was based primarily on two facts. Firstly, Brazil was not a democracy, but was instead a dictatorship ruled by Getúlio Vargas. Having come to power in a revolution during the early 1930s, Vargas had proclaimed a fascist 'new state' which invited obvious parallels with Italy, Spain and, to a certain extent, Germany. Vargas was also proud of his country’s independence, and this spawned the second factor: late in 1941, the USA requested the use of Brazilian bases for air operations, and to send in troops to guard these Brazilian bases against sabotage, but Vargas saw this as an affront to his nation’s sovereignty and refused. This may have been read in Washington more as a resistance to the USA than an indication of national pride. The result was the emergence of doubt about the course of Vargas’s, and thus Brazil’s, political ties.

There may also have been some truth to the fear that Brazil, or at least its military, would side with the Nazis. Most of Brazil’s military forces were based in the southern part of the country, for the northern part was relatively secure and therefore required little in the way of defence. While the Brazilian navy and air force were generally regarded as pro-Allied, which was hardly surprising given the ties that each had formed with the Royal Navy and the USAAC/USAAF respectively, there was a considerable support for the strong military example of Germany among the officer corps of the Brazilian army, which was based mainly in the South. Another factor in US thinking was the presence in Brazil of large expatriate German population, totalling perhaps 1.5 million persons, most of them in southern Brazil. The fall of France in June 1940 and the possibility of a German seizure of the Vichy French territories in West Africa completed the strategic scenario which presented itself to the US administration and government.

US planners believed that the German failure to capture Moscow late in 1941 could lead to expeditions on the opposite flank, resulting in a German offensive through Spain and Portugal, coupled with the seizure of Vichy French territory in Africa. This would bring Brazil within range of German aircraft, and led to the postulation of the arrival of German troops by air from Dakar in West Africa in combination with the mobilisation of pro-German elements of the Brazilian armed forces.

In the days after Pearl Harbor, therefore, the USA drafted plans to forestall any attempt to seize north-eastern Brazil for the Axis by a pre-emptive US seizure of the same area, and this was the genesis of the 'Rubber' plan.

The full title of the plan was the 'Joint Basic Plan for the Occupation of Northern Brazil [Joint], Serial 737 of 21 December 1941', and within this the initial part, dedicated to the seizure of several key ports and airports, was 'Rubber'. The object of 'Rubber' was to land US Marines in Brazil and on an outlying island to secure the vital airfields. The primary target was the airport at Natal, which was the primary airfield in the transatlantic link. Other mainland targets were Salvador in the south and Belém in the north, and also Fernando de Noronha island. All three of the mainland sites had airfields or airports capable of taking Boeing B-17 Flying Fortress heavy bombers and large transport aircraft. Fernando de Noronha island had a smaller airfield, but this had been built and was operated by the Italian airline Ala Littoria. Its strategic location, flanking the sea routes to Recife and Salvador, and the possibility of its use by Axis aircraft, combined to make the airfield a vital target. Two other targets deemed to be of great importance were the airfields at Fortaleza and Recife, though these were not scheduled for seizure from the sea.

From the very start, 'Rubber' was beset in planning terms by geographical considerations. With the exception of Salvador, which possesses wide sandy beaches, the Brazilian coast in the areas of Natal, Belém and Fernando de Noronha are almost totally unsuited to amphibious operations. At Natal, the beaches were sandy and shallow, and thus ideal in themselves for the use of landing craft, but were screened by a reef with only six gaps. This meant that landing craft would have to be launched nearly 9 miles (14.5 km) offshore, and finding the six gaps would probably be difficult. At Belém the situation was worse, for the best landing beaches were several miles from the city and divided from it by miles of impassable swamp. Apart from the docks at Belém itself, the only suitable landing points were some beaches closer to the city, but these could be reached only by landing craft (and then after an 8-mile (13-km) journey up the river) and were overlooked from the heights surrounding the city. If these heights were defended in any strength, the landings would be extremely hazardous. Finally, Fernando de Noronha island had only a single useful beach, and this was a mere 200 yards 185 km) wide and beset by a severe swell. Even an unopposed landing would have been treacherous, but if the beach was well defended it could have become a bloody killing ground.

Geographical factors were also the reason why Fortaleza and Recife could not be taken from the sea, for Fortaleza was surrounded by impassable terrain, and Recife was completely defended by reefs. Both would therefore have to be secured by overland advances from Natal after the initial landings.

Despite the significant problems which the geography of north-western Brazil presented, planning went ahead. Admiral Royal E. Ingersoll’s Atlantic Fleet would provide cover to the assault force, as well as shore bombardment using the battleship Texas and air support from the carrier Ranger, which could have embarked US Marine Corps squadrons tasked with ground attack in addition to her naval aircraft. The 5^th Marines and Major General Jacob L. Devers’s 9^th Division were allocated to the plan and began training for the expected amphibious assaults. In January 1942, troops of Major General Donald C. Cubbison’s 1^st Division and Major General Holland M. Smith’s 1^st Marine Division staged an exercise at Cape Henry, Virginia, in conditions that were more benign to those that could be expected at Recife. The result was a disaster, with navigation from ship to shore a particular problem: the troops were dispersed all along the beaches, organisation broke down and control was lost. In the eyes of the umpiring staff, the assault was a total failure, despite a 4/1 numerical advantage over the nominal defending force. What was worse, from the perspective of the 'Rubber' planners, was that the boat crews were those earmarked for the landings in Brazil.

However, the exercises did reveal a number of significant problems in the landing of troops from ships, and it is possible that some of these, now identified, could have been overcome by the time 'Rubber' was executed.

The US planners believed the Brazilian military to be sufficiently weak for the plan to succeed. At sea, Brazil could muster two British-built battleships, two light cruisers, nine destroyers, three submarines and a number of smaller craft. In the air, Brazil had nearly 330 aircraft, but many of these were obsolete. The number of aircraft reported as being in service at the time were 14 Boeing Model 256 and 46 Boeing Model 69 biplane fighters, 17 Vultee V-11 monoplane bombers, 12 V-11 monoplane torpedo bombers, six North American NA-44 attack aircraft and 10 Fairey Gordon biplane light bombers.

Like that of the army, the main strength of the Brazilian air force was concentrated mainly in the south, but could be quickly mobilised and sent to the north. In the regions to be seized, the Brazilians could muster about 3,500 troops at Natal, 2,900 at Fortaleza, 5,500 at Recife, 3,500 at Salvador and 1,300 at Belém. Fernando de Noronha island was a penal colony with only 65 guards, 600 inmates and 900 other inhabitants, but its airfield meant it could be reinforced rapidly by air. There were also a number of coast-defence installations, but the status of these was largely unknown to US planners. It was known that the Brazilians had drawn up plans for defences by mounting 12-in and 6-in (305- and 152-mm) guns, supported by mobile batteries with 75-mm (2,95-in) guns and machine guns, but whether or not these were in place at the time 'Rubber' is still a matter of debate. The Brazilians were as aware as anyone of the limitations imposed on coastal operations by their geography and as such it is likely that, if word of 'Rubber' had reached them, at least some form of defence would have awaited the attacking US forces.

In the event, no US landings took place in Brazil in 1942. There was a major effort on the diplomatic front, and this persuaded Vargas to allow US troops into Recife, which rendered 'Rubber' superfluous. In December 1941, Under-Secretary of State B. Sumer Welles persuaded Vargas to allow 150 US marines into the airfields at Recife, Natal and Belém, in the guise of aircraft mechanics. The marines were under instruction to guarantee the safety and security of the airfields and transiting US aircraft, but were reminded that they were there under the invitation of the Brazilian authorities.

This success sparked a fear that pro-Nazi elements in Brazil might occasion a backlash, but President Franklin D. Roosevelt resisted the urgings of some elements of his military staff for an immediately execution of 'Rubber', and instead sought a diplomatic solution. Roosevelt was quick to realise that Vargas needed to maintain the respect of his population, and thus had to save face, so Roosevelt’s moves were slowly and carefully arranged to allow this to happen.

At the very time when the US staff was planning to land troops in Brazil, Roosevelt ordered the export of guns and ammunition to Brazil, which raised the level of support for the Allies among the Brazilian government and military. This opened the way for a meeting of foreign ministers of the South American nations in January 1942, at which the US urged its neighbours to sever diplomatic relations with Germany. Increasing support for the Allied cause led to Brazil doing just that at the end of the meeting. The culmination of this careful policy was the signing in May 1942 of the Brazilian-American Defence Agreement, which allowed for full US support of the defence of Brazil, and finally (after five Brazilian merchant vessels had been sunk by U-boats) Brazil’s entry into the war on the Allied side on 22 August 1942.