The Royal Navy issues hazardous duty lifejackets to its personnel working on deck at sea. This lifejacket is designed to deploy as soon as it is immersed in water and means if a sailor is swept overboard at sea there is some chance of rescuing them. The problem arises, however, that the lifejacket is liable to become damaged or catch on something in the course of a sailor’s duties. As such as special cover is issued that covers the lifejacket and protects it from damage without impairing its function. This cover is made of blue nylon and has been made in a number of variations, this example being the Mk3: 

To help find a sailor swept overboard, a set of reflective patches are sewn to the chest: 

And at either shoulder: 

The cover has Velcro around all the edges to allow it to be secured over the lifejacket: 

A set of poppers is fitted to the bottom rear of the cover: 

This is used to secure the lifejacket at the point where a grab handle is provided so that the cover and lifejacket are securely fastened to one another. 

Loops are fitted to the side to allow the waist strap to pass through the cover: 

This is seen more clearly here on a commercial version of the cover: 

These covers are seen regularly being worn by sailors in the Royal navy and here two deck crew handling aircraft can be seen wearing the cover over their lifejackets: