Unfortunately the officer chosen to lead the advance on Costa Rica proved to be a knife more dangerous to the hand which held than to the breast before it. Colonel Louis Schlessinger was given the command, partly by way of compensation for the ill-treatment which he had received from the Costa Ricans when he went thither as one of the peace commissioners. Another of the commissioners named Arguello had deserted to the enemy. The third, Captain W. A. Sutter, son of the famous discoverer of gold in California, alone showed himself possessed of ability and honesty. Walker was not happy in his choice of civil officers, but it must be remembered that the supply of such material was limited. Heaven-inspired statesmen do not flock to the support of a cause so dangerous and unpromising as his.
If Schlessinger was a poor diplomat, he was a worse soldier. Starting with a force of two hundred men, he crossed the border of Guanacaste on the 19th of March. Five companies, of forty men each, had been divided, according to their nationalities or origin, into a French company, under Captain Legaye, a German under Prange, a New Orleans under Thorpe, a New York under Creighton, and a Californian under Rudler. The American companies comprised men of every English-speaking nation, "blown from the four parts of the earth." This division, which a skilful commander might have turned to account by exciting a generous rivalry, was but a source of weakness in the hands of the incapable Schlessinger, himself a foreigner and little popular with his men.
Their first and only engagement occurred at the Hacienda of Santa Rosa, twelve miles within the boundary of Guanacaste. Schlessinger allowed himself to be surprised, the enemy under a skilful officer, the Prussian Baron von Bulow, attacking him with a force of five hundred regulars, and winning an easy victory. Schlessinger did not even make a show of resistance, but ran away at the first shot, followed by the German and French companies. Captain Rudler and Major O'Neill made a brave stand with the New York and California companies, until some fifty of their command were killed, when the survivors made the best of their way off the field and across the border. Only a poor drummer-boy remained beating his drum with childish glee until shot down at his post. The wounded and the prisoners were all put to death by order of President Mora, who had proclaimed no quarter to every filibuster taken in arms. So ended the battle of Santa Rosa, on the 20th of March.