Previous Tatra units were concerned primarily with increasing capacity in a single tramcar.

Tatra sought to correct this shortcoming by developing its first articulated tramcar, the K1.

After a short trial in Prague with the prototype 7000, it entered Ostrava service with 800.

[1] The first prototype underwent reconstruction to functional sample KTX (later KT4) with a shortened body, in 1969.

After several test runs, it was retired and used as a warehouse in a Prague depot called Hloubětín.