Re: What defines an AAR boxcar?

Ed Hawkins

On Dec 15, 2006, at 12:48 PM, Kurt Laughlin wrote:

As best as I can tell, there were four main types: 1937, 1937
(modified), 1944, and postwar. What distinguishes theses from each
other? I'm pretty sure that 40-6 x 9-2 x 10-0 cars are the 1937 types
and that 40-6 x 9-4 x 10-6 cars are postwar, but what are the others
and how much leeway in dimensions is there within a type? For example,
looking at RPC 4 pages 12 to 34 I see:

NC &STL 18850 9-2 x 10-0 "1937 AAR"
CB&Q 35000 9-4 x 10-6 "AAR" (blt 5-47)
ATSF 143510 9-2 x 10-4 "1937 (modified) AAR"
CNW 71028 9-2 x 10-5 "1937 (modified) AAR"
CNW 80606 9-2 x 10-6 "1937 (modified) AAR"
UP 197899 9-2 x 10-6 "1944 AAR"
SOUTHERN 23399 9-2 x 10-6 "AAR" (blt 8-47)
MP 37447 9-2 x 10-6 "AAR" (blt 8-57)

Thanks in advance,
Since you specifically called out some RP CYC references, I'll comment
and provide some specific references. To begin, Richard and Tony are
right when they say it's not an easy question to answer!

For background, the Car Builders' Cyclopedias, which use A.A.R.
terminology, specify the "1937 A.A.R. design" (i.e., page 110 of the
1940 CBC). Generally, this design was for a standard 40'-6" box car
with 10'-0" IH (some variations existed). The majority of these cars
had Dreadnaught Steel Ends (4/5 corrugation pattern) and Murphy raised
panel roofs, however, there were box cars built that met the design
criteria having other ends and/or roofs (such as Buckeye ends,
Pullman-Standard Corrugated Ends, 5/5 Dreadnaught Steel Ends used by
CP, "NSC" ends used on numerous CN cars, Viking roofs). Prior to this
was the 1932 A.A.R. box car (originated by the A.R.A.), and a drawing
of this car is shown on page 113 of the 1940 CBC. The standard IH was
9'-4". Again, there were variations of the inside height, and there
were all kinds of variations of roofs and ends, causing this "standard"
car to be anything but standard from the standpoint of a plastic
manufacturer thus far unable to justify tooling cost. To this day we
have no good plastic models of the 1932 "standard design" box car that
Ted Culotta wrote an entire book about.

In the 1946 CBC is a drawing and photo of an Erie 40'-6" box car
(81000-81799), and it states "Modified A.A.R. Standard" on page 110 as
part of the drawing title. It also specifies "Modified 1937 A.A.R.
design" on page 111 as part of the photo caption. These cars had an
inside height of 10'-4 3/8", and they were essentially the same as the
1937 A.A.R. design except taller and used 5/5 Dreadnaught Steel Ends.
In my roster list of "Modified 1937 A.A.R. standard box cars," I
extended the definition to include A.A.R. design box cars with 5/5
Dreadnaught Steel Ends regardless of the inside height, basically to
cover cars from 10'-4" to 10'-6" IH. In 1941 the A.A.R. approved an
optional increase in the inside height from 10'-0" to 10'-6". Therefore
the earliest 10'-6" A.A.R. box cars are sometimes referred to as the
"1941 A.A.R. design," however I've not found any official use of this
term in a drawing notation. At any rate, references to the "Modified
1937 A.A.R." and "1941 A.A.R. design" should be considered synonymous
in their intent.

Now to the "postwar" terminology. First, the A.A.R. never used the term
"postwar" in their terminology that I know of. Moreover, I have never
found an official reference to anything called a "1944 A.A.R. standard
design." If anyone knows of an official source where the 1944 A.A.R.
terminology exists, please advise accordingly. The "1944 AAR"
terminology was used by C&BT Shops to identify their models, but the
term is strictly a modeler's term as far as I can tell. I believe the
reference Pat Wider used in RP CYC Volume 4 (UP box car caption) is
actually incorrect. This is something the proofreader (me) should have
caught and modified. The terminology should have been either the
generic use of "postwar" (lower case "p") or to leave off the year

All subsequent references in CBCs (1949/51 through 1960) are specified
as "A.A.R. Standard box cars" and they make no distinctions of the
variety of door opening sizes, roofs, and ends that were used. Per page
72 of the 1953 CBC, the Car Construction Committee revised the standard
box car designs in 1951 to show both a 6' and 8' door opening and to
incorporate other minor structural changes (drawing shown on page 76).
The 1953 CBC also stated that in Oct. 1947 the Car Construction
Committee revised the drawings of the 40'-6" box car to change the
inside height from 10'-0" to 10'-6" because "there had been little
demand for the 10'-0" height." Perhaps SP and B&O would argue that

Also during the postwar period was the widespread use of welded
underframes that had only limited usage on the cars of the 1937
designs. It's analogous to the AC&F Type 27 tank car. Once welded
underframes began being used by AC&F, the "Type 27" designation
disappeared with no new designation made, just the generic term "tank

As we know, "postwar" cars of 10'-4" to 10'-6" IH used a variety of
ends and roofs over 15+ years of production. In my rosters and
writings, I have used the term "postwar A.A.R. box car" not as an
official A.A.R. term, but to refer to a family of box cars generally
built from mid-1945 (first use of the Improved Dreadnaught End that I
could find) to 1960, where we cut off the discussion per STMFC
Ed Hawkins

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