When this helm is viewed, it is indistinguishable from a normal helmet, but detection will reveal it as magical, and the possessor will be able to both see and breathe under water. 

Visual properties of the helm are activated when small lenses are drawn across the device from compartments on either side of the helmet. They allow the wearer to see 5 times farther than normal water and light conditions allow for normal human vision. (Note that weeds, obstructions, etc. will block vision in the usual manner.) 

If the command word is spoken, the helm of underwater action creates a globe of air around the wearer's head, and maintains it, until the command word is again spoken. Thus, the wearer can breathe freely.