Soyuz 4

Three months prior, Kosmos 186 and Kosmos 188 achieved the first uncrewed docking of two Soyuz craft. The previous Soyuz flight (Soyuz 3) was also a docking attempt but failed for various reasons. The spacewalk was the only use of the Yastreb space suits. As well as mechnical docking, the crafts' electrical circuits were connected, and TASS announced the mission as the "world's first experimental cosmic station". The radio call sign of the crew was Amur, while Soyuz 5 was Baikal. This referred to the trans-Siberian railway project called the Baikal-Amur Mainline, which was in development at the time. The spacewalk crew transfer technique was intended to be repeated in the Soviet crewed lunar programs, to board the LK lunar lander design from the Soyuz 7K-LOK.