57 years after Chicago soldier recorded 8,600-word letter from Vietnam, Smithsonian preserves his voice and the sound of a passing helicopter

<img border="0" hspace="10" align="left" style="margin-top:3px;margin-right:5px;" src="https://timesofindia.indiatimes.com/photo/135259373.cms" />In March 1969, Frank A. Kowalczyk recorded an intimate 43-minute audio letter from Vietnam for