She usually makes him wears a claret and blue scarf with his Home Guard uniform, which supposedly prevents him from getting croup, even though only infants and (apparently) chickens are supposed to get it ("Menace from the Deep").
The passage describes a woman who compels her companion to wear a specific scarf while wearing his Home Guard uniform. The purpose of this action is to prevent him from getting croup, although the claim that only infants and (apparently) chickens are susceptible to it is mentioned in the narrative ("Menace from the Deep").