When he was ten, the family immigrated to the United States, settling in the Pennsylvania mining town of Wilkes-Barre, where his parents ran a small store.

He saw action in the Pacific Theater of World War II as an F4U Corsair pilot, serving in the Battle of Okinawa and in bombing missions over Japan.

[4][6] After learning that 14 relatives including his grandmother 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.

[7][8][9] After the war, Lenart participated in Operation Ezra and Nehemiah, the airlift of Iraqi Jews to Israel in the early 1950s, served as a pilot for El Al, and flew aerial mapping missions over the jungles of Central America.