An operation with the codename Plan Rubber was the amphibious component of the Joint Basic Plan for the Occupation of Northeast Brazil, J. B., Serial 737, dated 21 December 1941. This would have been a United States military invasion of the northeastern coast of Brazil, through the beaches of Natal, during World War II. The plan was never carried out due to successful diplomatic initiatives with Brazilian President Getúlio Vargas.
Brazil's northeastern salient or bulge is where South America is at its closest to Africa, and thus offered American strategists an air route through the Atlantic Ocean and a platform for maritime patrol in the Battle of the Atlantic. Since the late 1930s, the region was part of the US's defensive perimeter as defined by its military planners. Since 1941 the Brazilian Armed Forces were reinforcing their hitherto almost undefended coastline north of Rio de Janeiro, but officials in the American Franklin D. Roosevelt administration deemed these defenses insufficient and feared the Brazilian Estado Novo dictatorship would align itself with the Axis powers or be overthrown by a pro-Axis coup.
A land intervention in Brazil was studied by previous plans such as May 1940's "Pot of Gold" and November 1941's "Lilac". Plan Rubber had its main goal in the city of Natal, which would be occupied by the US Marine Corps. US Army reinforcements would proceed by land to Fortaleza and Recife. Further landings would occupy Belém, Salvador and Fernando de Noronha. Brazil's Army, Navy and Air Force were deemed unprepared for an effective defense, and Brazilian reinforcements would have to come from the south in an eight to twelve-day movement by sea. Nevertheless, difficult geography on the beaches (except in Salvador) and unprepared landing craft crews could cause high casualties.
Military planning offered alternatives in case diplomatic negotiation failed. The latter was already producing results months before Brazil's entry into the Second World War on the American side in August 1942. The US Armed Forces were allowed to operate in air and naval bases in the Brazilian bulge, rendering invasion plans unnecessary. Parnamirim airfield, on Natal's outskirts, became one of the busiest American air bases in the war.
American concerns over Brazil
Geographic relevance
Already in 1938, prior to the outbreak of war, American military planners studied a conflict with Germany, Italy and Japan, which would later comprise the Axis powers. Some placed the defensive perimeter of the United States as far as the 10th parallel south in South America, which would include the Brazilian bulge but neglect the Southern Cone. This corresponds to the concept of a "Quarter Sphere" with corners in Newfoundland, Alaska, the Galapagos Islands and northeastern Brazil. The Quarter Sphere is distinct from the traditional "American lake" (an exclusive defense of the continental United States and Caribbean) and "hemispheric defense", which would cover the entire American continent.
An enemy-controlled Galápagos or Brazilian bulge would threaten the Panama Canal. Far eastern Brazil is South America's closest point to Africa, down to a minimum of 2900 kilometers between Natal and Dakar. The imaginary line between both cities is known as the "Atlantic Narrows" and is one of the definitions of the border between the North and South Atlantic. The Narrows are a convenient position to split the two halves of the Atlantic or cross from one continent to another. Aircraft of this period could cover the gap in eight hours. The development of air power and the Africa-Natal air route changed calculations in the defense of the Western hemisphere. American strategists saw Natal as the likely bridgehead in a German invasion of Brazil.
In January 1939, Under Secretary of State Sumner Welles brought up the possibility of a pro-German coup in Brazil, followed by a German invasion through the Atlantic Narrows. This scenario was used in the Navy's Fleet Problem Exercise in the fall. German pressure over Vichy France after 1940 created concern over a potential Wehrmacht presence in French West Africa, including Dakar. This city's distance from Natal was less than half of the distance between Natal and Norfolk, Virginia. It is controversial if German intentions of an attack on the US through Africa existed in the first place. A 1960 publication by the US Army's Center of Military History observed there were German plans for Spain, Gibraltar (Operation Felix) and Morocco, but no evidence they extended to a transcontinental invasion of Brazil. And yet American planners saw such an invasion as the logical next step after Africa. Historian Frank McCann states German limitations made this invasion a fantasy, but American planners had to work with imperfect information and worst-case scenarios.
The South Atlantic became the only viable air route towards North Africa and Europe in December 1941. The Japanese attack on Pearl Harbor moved the United States directly into the global conflict, which had involved essentially European powers and their colonies, and interrupted the air route towards general Douglas MacArthur's besieged troops in the Philippines. Winter interrupted traffic over the North Atlantic. Airports in Natal and Recife were less than 1750 nautical miles from Freetown, Sierra Leone, through which transport aircraft of the United States Army Air Corps could deliver priority cargo, personnel and the planes themselves to North Africa, the Middle East, India, Burma, China and the Philippines. Furthermore, naval and air bases in the region could be used in the Battle of the Atlantic for patrols against the German U-boat threat to navigation.
Vulnerable defenses
American planners feared the vulnerability of Brazilian defenses in the northeast and the country as a whole. A Department of War analysis in January 1939 found the coastal cities to be "almost completely defenseless", and air defense did not exist, not even in Rio de Janeiro and São Paulo. This comment might have been exaggerated, but Brazil's military weakness was real. The Brazilian Army's 60 thousand men in 1939 lacked modern armament and were concentrated south of the capital, neglecting 2500 miles of coastline to the north. The US Army believed only an American ground presence would be enough to defend the region. Brazilian land and air defenses couldn't resist a modern combat force.
Prior to April 1941, the Brazilian Army's presence in the 7th Military Region, comprising the northeastern states of Alagoas, Pernambuco, Paraíba, Rio Grande do Norte, Ceará, Piauí and Maranhão, was mostly limited to a battalion of caçadores (light infantry) in each state capital. From 1940 to 1943, this regional command was under general Mascarenhas de Morais, who would later command the Brazilian Expeditionary Force. General Estevão Leitão de Carvalho assumed command of the East and Northeast Theater of Operations (), which oversaw the 7th and 6th (Bahia and Sergipe) Military Regions, in February 1942.
In a February 1941 correspondence to the US, military attaché Lehman W. Miller argued American servicemen should not be sent to Brazil until the country felt itself threatened, as Brazilian public opinion was hostile to the Axis, but sensitive to a violation of their national sovereignty. And yet the US Army's fear was precisely that Brazil wouldn't react in time. Brazil's Minister of War, Eurico Gaspar Dutra, and Army Chief of Staff, Góis Monteiro, recognized the northeast was vulnerable; their fellow officers desired to strengthen their institution and defend their territory without relying on American assistance on land. But the country's low level of industrialization meant any rearmament relied on foreign suppliers, be they German or American.
In the course of several years, the Brazilian Ministry of War concentrated an unprecedented troop strength in the northeast. Reservists began to be called up in the region on the 24th of July, 1941. Far-away units were moved to the northeast and transformed or absorbed by others. The transport of personnel and equipment took place by sea, a route which would prove itself vulnerable when German U-Boats torpedoed Brazilian ships in 1942. There were no railways or highways connecting the north and south of the country, and this was the major weakness of the northeastern theater of operations. The safer alternative, transport over the São Francisco river, would have to rely on neglected infrastructure.
In December 1941, the Natal garrison comprised the 16th Infantry Regiment, 1st Company of the 1st Engineering Battalion and 4th Pack Artillery Group, equipped with two batteries of Schneider 75 millimeter guns. The 1st Group of the 3rd Antiaircraft Artillery Regiment, with two batteries of Krupp 88 mm, arrived on the 15th of January, 1942. The João Pessoa garrison comprised the 15th Infantry Regiment and the 3rd Battery of the 4th Pack Artillery Group. Inland Paraíba had the 22nd Caçadores Battalion in Campina Grande, where the 1st Howitzer Group arrived on January 6, 1942. Fortaleza was defended by the prewar 23rd Battalion of Caçadores and a reformed 29th Battalion of Caçadores. The Maceió, São Luís, and Teresina garrisons each consisted of the 20th, 24th and 25th Caçadores battalions, all of them prewar formations.
Recife and nearby Olinda were garrisoned by the 14th Infantry Regiment, the 2nd Independent Guard Company, the Antiaircraft Machine Gun Battery, the 2nd Independent Motorized Artillery Battery, and the 4th Independent Transport Company. The two batteries and the 3rd Battery of the 4th Pack Artillery Group were unified in the Independent Mixed Artillery Group, based in Olinda, on January 2. The machine gun battery, the only one in the northeast, was described by an inspection in April as all but deprived of ammunition, and national production was an unresolved problem. The 3rd Motorized Supply Train Squadron was organized in February 1942 and the Moto-Mechanized Wing of the 7th Divisional Cavalry Regiment in the following month. Inland Pernambuco had the 21st Battalion of Caçadores in Caruaru.
The Fernando de Noronha archipelago was initially undefended. A Navy garrison was discussed in 1941, but the Navy's marines lacked the equipment for a proper defense. Admiral Alberto Lemos Bastos, commander of the 2nd Naval District based at Salvador, wrote in a letter to Vargas: "the occupation of Fernando de Noronha should be, I believe, made by the Navy. When I told this to the Minister [of the Navy], he told me the Navy couldn't do it". The garrison would eventually be provided by the Army. The 30th and 31st Caçadores battalions, earmarked for defense of the archipelago, began to be organized in Olinda and Recife in December 1941. Alongside the 1st Mobile Coast Artillery Group, 1st Group of the 2nd Antiaircraft Artillery Regiment, 1st Independent Howitzer Battery and supporting elements, they landed on the archipelago between April 6 and July 9, 1942. The 1st Mobile Coast Artillery Group was one of several new units of American-equipped coast artillery units in 1942. The 2nd and 3rd Groups, respectively designated for Natal and Olinda, would be created on June 26.
Raw materials Brazil was also a provider of raw materials to the increasing demand of the American war industry, such as rubber, bauxite, beryllium, chromite, iron-nickel, industrial diamonds, manganese ore, mica, quartz crystals, titanium, zirconium, cobalt, tungsten, nickel ore, tantalite, columbite, and castor oil. Brazilian rubber replaced Asian providers cut off by Japan's entry to the war. An Axis occupation of the northeastern salient would separate the US from South America's natural resources.
Axis influence in the government