Tim,

ACF wasn’t the only builder of cars of this type that were primarily used for chlorine containers. ACF records document the company built approximately 350 "Multi-Unit Tank Cars" from 1924 to 1958 comprised of 87 orders having lot numbers assigned. Roughly half of the cars were built before 1940 with the largest pre-1940 order being 16 cars.

Ten of these cars were built “for stock” for the U.S.A. Chief of Engineers. I don’t know the disposition of these lot 2370 cars built in July 1941. 

Six ACF builder photos of these cars are on the Barriger Flickr web site with 3/4-views & “B” end views of 3 of the earliest cars - lot 10, MALX 365; lot 188, VSX 204; lot 401, GWEX 4?? (angled view hides car number). 

List of ACF M-U tank cars by reporting marks to include the quantity of cars, number of orders, and range of build dates:

ACCX - 10 cars, 4 lots 1926-1935

ACF - 10 cars, 1 lot, built 1941 (U.S.A. Chief of Engineers)

BAKX - 2 cars, 2 lots 1931-1932

BCX - 7 cars, 3 lots 1926-1931

CACX (or possibly PPGX) - 21 cars, 2 lots 1936-1937

CALX - 3 cars, 3 lots 1927-1934

CILX (Canada) - 2 cars, 2 lots 1932, 1945

DAX - 23 cars, 11 lots 1928-1946

DUPX - 15 cars, 3 lots 1926-1933

GCX - 26 cars, 1 lot, built 1948

GWEX - 8 cars, 2 lots 1927-1928

HOKX - 8 cars, 2 lots 1925-1926

MALX - 10 cars, 1 lot, built 1925

MONX - 7 cars, 3 lots 1932-1936

PSMX - 32 cars, 12 lots 1924-1948

SHPX - 101 cars, 16 lots 1937-1948 (lessees - Westvaco, DuPont, Diamond Chemical, likely others)

SPX - 44 cars, 11 lots 1927-1948

TELX - 1 car, 1 lot, built 1930

TENX - 4 cars, 1 lot, built 1949 (for sulphur dioxide containers)

VSX - 15 cars, 5 lots 1924-1929

WCX - 1 car, 1 lot, built 1930? (unsure about this order)

Regards,

Ed Hawkins