On 5 December 1928, a Paraguayan Major Rafael Franco, angered by his country's inactivity in the Chaco in the face of Bolivian encroachment and disregarding standing orders to avoid contact with the Bolivian Army, led an attack against Fortin Vanguardia on the upper Paraguay River. This precipitated a diplomatic and military crisis.

Nine days later, Bolivia retaliated by capturing Fortin Boqueron in the central Chaco, after calling up reserves and reinforcing garrisons. In turn, on 17 December, Paraguay reorganized its Chaco forces into 3 sectors [North, Central and South] as part of a massive mobilization, increasing its establishment there to 19 infantry Regiments, several Cavalry Units and 4 Batteries of Artillery.

Only the fortuitous failure of mobilization on both sides due to chaotic plans, lack of arms, [neither having received the bulk of their 1927 arms purchases] and inadequate transportation networks [particularly from the Bolivian "Altiplano" to the Chaco lowland] prevented full-scale war.

Although both counties reduced their military establishment under a ceasefire agreement [Paraguay to 7 Regiments including 1 Cavalry, 4 of these being based in the Chaco, while Bolivia to 6,000 soldiers in 6 Divisions, with some 1200 stationed in the Chaco], each continued a comprehensive plan of exploration of the Chaco. Between 1929 and 1932, Bolivia established a line of Fortines through the Central and Northern Chaco regions. Paraguay reciprocated by placing Fortines so that they blocked Bolivia's attempts to move east and south and protected a significant economic investment in the area.

In January 1930, a Bolivian plan of attack against Paraguayan Fortines in the crucial Central Chaco was halted at the last minute when Paraguayan cryptographers released copies of the documents to the international press. Even after diplomatic reconciliation, tensions continued to run high. Between the beginning of 1930 and the end of 1931, the Bolivian Army documented some thirty minor clashes [4].

Both countries continued an arms buildup, with the arrival of the remainder of its Vickers contract, Bolivia ordered additional Curtiss-Wright combat aircraft and impressed part of Lloyd Aereo Boliviano's transport fleet, the country's largest airline. Paraguay purchased another 7,000 Mauser rifles, 200 machine guns, 24 Stokes-Brandt 81mm mortars and a few combat aircraft. By June 1932, Bolivia's Army consisted of approximately 5,500 troops [against an establishment by law of 9,460] [5], 50,000 rifles, 1,000 machine guns, 80 Artillery, and 50 combat aircraft, Paraguay had 3,000 soldiers [establishment being 5,000], 17,000 rifles, 425 machine guns, 48 artillery, 24 mortars, 5 river gunboats and 12 combat aircraft.

In June 1932, the dispute escalated into full-scale conflict, the precipitating factor was the Paraguayan discovery, in March 1930, of Lake Pitiatuta in the Central Chaco. Pitiantuta's year-round water supply [a rarity in the Chaco] had strategic importance for possible development of the area. In addition its discovery moved Paraguayan territorial claims substantially westward, in July 1931, Paraguay built Fortin Carlos Antonio Lopez on the east shores of the lake. Bolivia discovered this lake only in April 1932 during an air reconnaissance mission, although buildings thought to be Paraguayan could he seen on the eastern shores of the lake, in mid-May, a Bolivian Army detachment was ordered [whether by President Salamanca or Army Chief of Staff Osorio is unclear] to occupy the site. On 15 June, the Bolivian force attacked the Paraguayan Fortin.

NOTES:

[1]. Fortines are military posts, consisting of a few huts and perhaps a ditch and fortifications, manned by 5 to 500 men.
[2]. Carlos Jose Fernandez, pp.40-41. Adrian English, Armed Forces of Latin America [london: Jane's, 1984], pp.76-85.
[3]. Fernandez, Ibid., pp.26-27. English, Ibid., pp.348-60.
[4]. Most of the clashes were unintentional, the result of too many soldiers, with too many guns, in too small an area.
[5]. English, bid., pp.76.