A Havelock hat is a military cap cover with a flap at the back for sun-protection of the neck and ears. It was made of linen and was worn on top of the cap for sun protection. However, the soldiers found it useless because it added to their weight and also restricted air-circulation, thus increasing their body temperature. They even went to the extent of using Havelock as a tea or coffee strainer.
Another way of creating a Havelock was to place a handkerchief on the head and wear a cap on it. It would also protect the neck, but it could be made impromptu and on a need basis. Later on, some caps were manufactured with the flap incorporated, and these were also known as Havelock hats.