Soyuz 7K-TM was a two-seat Soviet Soyuz variant developed for the Apollo-Soyuz Test Project, with mission-specific rendezvous, docking, and environmental-control systems. Soyuz 16 performed the crewed rehearsal in 1974, Soyuz 19 completed the international docking in 1975, and the backup spacecraft flew as Soyuz 22 in 1976 after adaptation for Earth observation.