After learning that 14 relatives had been murdered in the Auschwitz concentration camp and attending a lecture on Zionism, Lenart decided to volunteer for Sherut Avir, the precursor to the Israeli Air Force.
On May 29, 1948, Lenart took part in Operation Pleshet, when the Israeli Air Force launched its entire fleet of four fighter aircraft in a desperate attempt to halt an Egyptian advance on Tel Aviv, in coordination with a ground counterattack.