Ernst arrived in Budapest in 1941 and, that same year, he joined the movement in the Újpest suburb of the capital. In 1943 he met Neshka Goldfarb and later, Tzvi Goldfarb, Vili Eisikovics and other comrades. Under a false name and with forged documents he started working for the underground. He went on missions to the forced labor camps in order to smuggle comrades into Budapest. He walked around the city wearing the uniform of a lieutenant of the pre-army “Levente” and, according to a list he had, Ernst took Jews out of the ghetto. Riding a motorcycle he maintained contact with the bunkers and supplied food and equipment for them. Ernst was arrested by fascist Arrow Cross men and taken to their headquarters on 60, Andrássy Street. Afterwards he was taken for further interrogation to the Gestapo headquarters in Buda. When he was being taken with a group of Jews to the banks of the Danube where the fascists intended to shoot them, Ernst succeeded to escape and arrive in one of the bunkers in Buda. However, he found out that the bunker had already been discovered by the Hungarian police. In a park in the vicinity of the Eastern Railway Station he met with Vili Eisikovics who led him to a nearby different bunker of the movement. Two days later that bunker too was discovered and its occupants were taken to the prison on Margit Boulevard. He underwent cruel interrogation and eventually was liberated by a daring operation of the underground Zionist Youth Movement and taken to one of the Protected Houses where he was liberated by the Red Army.
Ernst made aliya. Nowadays he lives in the USA.