I found a knitting pattern for a Winter Sock in the January 1860 Godey's. It supposes a certain amount of knitting knowledge, which is typical of patterns of the time.
Note the needle size; it looks like No. 18. This does not work for either U.S. or British size needles. Most likely, it is a Size 13 British, which would be a Size 0 in U.S.
Also, from an 1861 issue of Scientific American:
THE WAR.
The government calls upon the loyal women of
America to knit stockings for our brave soldiers. The
following rules are laid down for the direction of
ladies wishing to knit socks for the soldiers:—Get
large needles and a coarse yarn; cast on seventy-eight
stitches, and knit the leg ten inches before setting the
heel. The heel should be three and a half inches
long, and knit of double yarn, one fine and one
coarse, for extra strength. The foot should be eleven
or twelve inches long.
1861 Issue: 10/26 Page Range: 0258ad-0259a
Scientific American, 10/26/1861
Kat in NJ