The Crew Return Vehicle (CRV), sometimes referred to as the Assured Crew Return Vehicle (ACRV), was a proposed dedicated lifeboat or escape module for the International Space Station (ISS). A number of different vehicles and designs were considered over two decades – with several flying as developmental test prototypes – but none became operational. Since the arrival of the first permanent crew to the ISS in 2000, the emergency return capability has been fulfilled by Soyuz spacecraft rotated every 6 months.