The havelock was first used by the British army in the Sepoy rebellion in India. It was adopted by the French Foreign Legion and also used by Americans in the Civil War.
The trick to making a 1:6 havelock is sewing a smooth curve where the sides meet the crown.
1. Sew sides together along the back seam.
2. Hem bottom of sides.
3. Hem sides of drape & if desired hem bottom.
4. Sew drape to bottom of sides. Fold the drape over to find the center. Line up center with the back seam. Start sewing at back seam and go to front. Start at back seam again going the other way and sew to front.
5. Sew crown to top of sides. Sew two or three stitches, reposition, sew three more, reposition; to keep the curve smooth. Start at back seam and go to the front. Leave a space at the end for the front seam. Repeat for other side.
6. Sew sides together at front; straight up & down. If necessary stitch where top of front meets crown.
Turn outside out; you're done!
(The brim isn't necessary for the havelock; but can be used to make a forage cap with the pattern)