You may want to refer to the knitting instructions from 1918.
# 5 One-Piece Helmet
One hank of yarn (¼ pound); Red Cross needles No. 2.
Cast on 56 stitches loosely. Knit plain for 8 inches for front piece, and leave on extra needle. Knit another piece to correspond for back. These pieces must be at least 9 inches wide. Slip the stitches of both pieces on to 3 needles, arranging for last 2 stitches of back piece to be on beginning of 1st needle, with 38 stitches of front piece added (making 40 on 1st needle).
Divide rest of stitches on other 2 needles; 36—36.
Beginning with 1st needle, knit 2, purl 2 for 6 inches. Then on 1st needle knit 2, purl 2 for 18 stitches. Bind off 22 stitches for face opening. (Try to keep same arrangement of stitches on needles for further directions.) Knit 2, purl 2 forward and back on remaining 90 stitches for 1½ inches, always slipping first stitch. Cast on 22 stitches loosely to complete face opening, and knit 2, purl 2 for 2½ inches (adjust stitches by slipping 2 from end of 3d needle to 1st needle, making 42 on 1st needle).
Knit 1 round plain. Knit 2 stitches together, knit 11, knit 2 stitches together, knit 1. Repeat to end of round. Knit 4 rows plain. Then knit 2 stitches together, knit 9, knit 2 together, knit 1. Repeat to end of round. Knit 4 rows plain. Continue in this way, narrowing on every fifth round and reducing number of stitches between narrowed stitches by 2 (as 7, 5, 3, etc.) until you have 28 stitches left on needles. Divide on 2 needles, having 14 on 1st needle and 14 on the other.
Break off yarn, leaving 12-inch end. Thread into worsted-needle and proceed to weave the front and back together as follows:
* Pass worsted-needle through 1st stitch of front knitting-needle as if knitting, and slip stitch off—pass through 2d stitch as if purling—leave stitch on, pass thread through 1st stitch of back needle as if purling, slip stitch off, pass thread through 2d stitch of back needle as if knitting, leave stitch on. Repeat from * until all the stitches are off the needle.