Manufactured by Pacific Car & Foundry Co., it was a substantial upgrade over the Diamond T M19 transporter/trailer duo introduced in 1940.

Designed by the Fruehauf Trailer Company of Detroit, Michigan,[4] it was heavier than the Diamond T could manage.

When it could not keep up with the Army's demands, production was awarded to the Pacific Car & Foundry Co. of Seattle, Washington.

[4] Unusually, the tractor unit was fitted with both an armored cab and two winches with a combined pull of 60 tons,[4] allowing it to do light battlefield recovery work.

An experimental ballast tractor conversion was evaluated by the British Fighting Vehicle Proving Establishment[4] After the war, some of them (both armored and unarmored) were bought as surplus and used to carry oversize loads such as transformers, locomotives and heavy equipment.