Aircraft in Vietnam

This strange-looking Lockheed aircraft was designated a YO-3. I saw only a few of them in-country and never saw any outside of Vietnam. It was operated by the Army and was designed to be very acoustically quiet. This is evidenced by the large wooden six blade prop and the fact that it is the only piston aircraft I have ever seen with a muffler! The round object in the belly appears to be an infrared sensor. I expect it was used at night to locate bad guys by their heat signatures.
I was informed by an authority on Army aircraft that  they were used after the war by several agencies such as the Border Patrol and Customs on border interdiction duties, and also at least one was used by NASA to act as an airborne microphone holder to test other aircraft for their noise patterns as part of noise abatement studies. 
Revised: 24 March 1999