Johan was a member of the "Mountain Howitzer and Rocket Battery" made up of Ordnance Corps soldiers in 1846. The battery was part of General Scott's invasion at Vera Cruz, and he participated in the Battle of Cerro Gordo.

Months later he was killed in action during the Battle of Contreras on 19 August 1847 just south of Mexico City. It was a fierce fight against 22 Mexican cannon of larger caliber and the outcome was inevitable.

Frederich Zeh, a member of the battery, wrote that he was a "gallant and valiant soldier in every respect."

He described how Ungerer, who he misnamed "Unscheler" as his memory faded, left his hospital wagon and rejoined the battery for the fight, not wanting to let them down, the doctors could not stop him. He also wrote that Ungerer was mortally wounded and died shortly afterward.

They could not bury the dead behind their battery position due to the nature of the volcanic terrain, so they piled loose rocks over them as a grave.

It is unknown if he was ever reinterred in the American Cemetery near the "English Cemetery" which was constructed after the war. Those soldiers were reinterred in a mass grave. If not, his bones remain at the south edge of the "Pedregal."

A month after the battle, A. A. Manning sent a letter inquiring as to the whereabouts of several soldiers from his hometown, it is among the documents on this page.

Johan Ungerer