In 1949 the US Army set a requirement for a family of extra heavy-duty 10‑ton (9,072 kg) load rated, off-road, 6x6 tactical trucks.

In addition to the US Army, the M123 was used by the U.S. Marine Corps and exported to U.S. allies in such countries as Australia and Spain.

The transfer case had a 2.50:1 low range, engaged the front axle, and had a power take-off to operate the winch(es).

[3][1][7][8] The front axle was an unusual triple reduction type which did not need universal joints on the outer ends and allowed a tighter turning radius.

It had a higher load plate and larger coupling pin than a standard semi-trailer.

It had hinged doors with roll-up windows, a folding windshield, and a removable canvas roof.

Variants: The M125 succeeded the Mack NO as a heavy cargo transport vehicle; it also served as a prime mover towing the 155‑mm gun and 8‑in.

It had a 14 ft (4.27 m) steel cargo body with folding troop seats, bows and canvas cover.

A single front-mounted Garwood DSA716 45,000 lb (20,000 kg) capacity winch was fitted, and a chain hoist at rear for handling ammunition.