Trench Whistles, Police Whistles, English Bobbie Whistles, and Tubular General Service Whistles. These are all names for the for a whistle instrument that has been used in wars, blown by police and played with by countless children and of course adults.
The most common form of these Trench whistles was made by a company called J Hudson & Company. There were other companies including A.De Courcy & Co who also resided in Birmingham, England.
Below is a cool video that shows you how these whistles are actually made.