Soldiers camped overnight with no fuel for warmth, as the temperature fell to 7° Fahrenheit (-14° Celsius). There were over 900 cases of frostbite, and 2,000 casualties on the French side. On the Prussian side, there were less than 500 dead. On 19 January a final breakout attempt was aimed at the Château of Buzenval in Rueil-Malmaison near the Prussian Headquarters, west of Paris. The Crown Prince easily repulsed the attack inflicting over 4,000 casualties while suffering just over 600. Trochu resigned as governor and left General Joseph Vinoy with 146,000 defenders. During the winter, tensions began to arise in the Prussian high command. Field-Marshal Helmuth von Moltke and General Leonhard, Count von Blumenthal, who commanded the siege, were primarily concerned with a methodical siege that would destroy the detached forts around the city and slowly strangle the defending forces with a minimum of German casualties. But as time wore on, there was growing concern that a prolonged war was placing too much strain on the German economy and that an extended siege would convince the French Government of National Defense that Prussia could still be beaten. A prolonged campaign would also allow France time to reconstitute a new army and convince neutral powers to enter the war against Prussia. To Bismarck, Paris was the key to breaking the power of the intransigent republican leaders of France, ending the war in a timely manner, and securing peace terms favourable to Prussia. Moltke was also worried that insufficient winter supplies were reaching the German armies investing the city, as diseases such as tuberculosis were breaking out amongst the besieging soldiers. In addition, the siege operations competed with the demands of the ongoing Loire Campaign against the remaining French field armies. Air medical transport is often stated to have first occurred in 1870 during the siege of Paris when 160 wounded French soldiers were evacuated from the city by hot-air balloon, but this myth has been definitively disproven by full review of the crew and passenger records of each balloon which left Paris during the siege. During the siege, the only head of diplomatic mission from a major power who remained in Paris was United States Minister to France, Elihu B. Washburne. As a representative of a neutral country, Washburne was able to play a unique role in the conflict, becoming one of the few channels of communication into and out of