Aircraft Warning Service Observation Tower, Military observation tower in Agnew, United States.

The Aircraft Warning Service Observation Tower is a three-story wooden structure with exterior staircases and large windows on its top level. The tower features a surrounding observation balcony designed for clear views across the landscape.

The tower was built in 1941 and served as a spotting station during World War II to monitor potential Japanese aircraft. It was part of a nationwide air defense network that protected the western United States.

Jean Cook, named chief observer, organized 300 volunteers from the Cook farmhouse to keep a 24-hour watch and report to the Port Angeles filter center, which relayed sightings to the U.S. Army. The tower's name comes from this Aircraft Warning Service program, active from 1941 to October 1943.

The tower stands on private property in Agnew, at the end of a rural road off U.S. Route 101. It is a fragile 1941 wood-frame structure with an exterior stairway, so it is best viewed from the roadside rather than entered. The site is a short drive east of Port Angeles.

The tower was built behind the Fred and Jean Cook farmhouse from donated materials, and Jean Cook organized 300 volunteers to keep a 24-hour watch. It is the only surviving Aircraft Warning Service tower in Clallam County.