This is an unflown Mark 4 reentry vehicle (RV) used on U.S. Air Force Titan I and Atlas E/F intercontinental ballistic missiles that were deployed in the early 1960s. It carried a W-38 nuclear warhead with a yield of about 3.75 megatons. Made by AVCO Corporation, the Mark 4 RV has an aluminum inner frame covered by an unknown ablative material that protected it during reentry into the Earth's atmosphere. Because R&D versions of reentry vehicles were commonly painted white, this Mark 4 RV was in all likelihood a test version that was never flown. The donor is unknown.