On this day in 1969, the Soviet space programme accomplished the first docking of two vessels in orbit.
The three cosmonauts of the Soyuz 5 joined the crew of two in Soyuz 4 and transferred two members between the capsules through an airlock. The objective of the previous three Soyuz missions had been to demonstrate the technical feasibility of linking two modules but had been aborted for various reasons. This achievement paved the way for later cooperative and international missions. During a celebratory parade in Moscow a week later, the cosmonauts sustained light injuries during an assassination attempt whose target was Secretary Brezhnev who was riding in their motorcade. The failed attempt was subject to a Soviet media blackout for years afterwards.