Cairo Skywatch Tower, Cold War observation tower in Tippecanoe Township, Indiana, US.

The Cairo Skywatch Tower is a 40-foot wooden watchtower in Tippecanoe Township, Tippecanoe County, Indiana. It once had a glass-enclosed office at the top, and it is also known as Delta Lima 3 Green Ground Observation Tower.

Built in 1952, the 40-foot wooden tower was the first officially commissioned rural skywatch tower of the U.S. Air Force's Civilian Ground Observation Corps under Operation Skywatch. It was abandoned in 1959 after the corps dissolved, and listed on the National Register of Historic Places in 2002.

The tower's alternate name, Delta Lima 3 Green Ground Observation Tower, comes from the radio call sign used in the Ground Observation Corps network. Volunteers of the corps watched the skies from such posts and reported aircraft sightings; the Cairo post was the first rural tower the Air Force officially commissioned for this duty.

The tower stands in Tippecanoe Township at the corner of County Road 850N and County Road 100W, north of the unincorporated community of Cairo. It is a 40-foot wooden structure with no glass office remaining, so it is viewed from the outside rather than climbed. The site is listed on the National Register of Historic Places.

The tower's official designation was Delta Lima 3 Green Ground Observation Tower, a call sign used in the Skywatch network. It was the first rural tower officially commissioned by the Air Force's Civilian Ground Observation Corps, and after the corps dissolved in 1959 it stood abandoned until its 2002 listing.