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The earliest known actual walking dragline was from Ransomes & Rapier 1939 using the patented Cameron and Heath  walking method. Model W170, it had a 4-yard bucket.

TRACTION OR PROPULSION MECHANISM OF THE WALKING TYPE –  Cameron et al.

Colin McLeod Cameron and Alfred Thomas Heath

British Patent 320,223
Granted Feb 21, 1940.
Filed Mar 3, 1939.

See US Patent here.

US Patent number: 2259200
Filing date: Feb 21, 1940
Issue date: Oct 1941

There was an earlier patent by Vincent G. Anderson in 1918 where he proposed a walking dragline or excavator resulting in a similar walking and steering fashion.

Patent number: 1455380
Filing date: Apr 22, 1918
Issue date: May 15, 1923
See here.

Bacyrus-Erie took over Ransomes & Rapier  in 1988 and continued to use this method of propulsion for these gigantic land machines.

"Big Muskie"

Big Muskie was a coal mining Bucyrus-Erie dragline owned by the Central Ohio Coal Company (formerly a division of American Electric Power), weighing nearly 13,000 metric tons (13,000 long tons; 14,000 short tons) and standing nearly 22 stories tall. It operated in the U.S. state of Ohio from 1969 to 1991.

The Big Muskie was a model 4250-W Bucyrus-Erie dragline (the only one ever built). With a 220 cubic yards (170 m3) bucket, it was the largest single-bucket digging machine ever created and one of the world's largest mobile earth-moving machines. Its bucket could hold two Greyhound buses side by side. It took over 200,000 man hours to construct over a period of about two years.