On 13 January 1881, Otto participated in the Battle of San Juan and Chorrillos, commanding the 4th Company of the 1st Battalion of the Regiment Chacabuco, which was part of the Amunátegui Brigade of the 1st Army Division in the battle, under Patricio Lynch. During the second phase of the battle, after Chilean forces captured the San Juan line, his regiment and the Regiment 4th Line were ordered to attack the strong Peruvian defences on the Morro Solar promontory. Otto did the same at the head of the company he commanded. In that place the Chilean forces were repelled with several casualties by the intense fire, having to retreat and abandon some trenches that they had managed to occupy in the face of the Peruvian counterattack. It is during this part of the battle that he is mortally wounded by a gunshot to the chest, and then his body is cruelly torn to pieces on the ground by Peruvian soldiers with rifle butts and knives.