The pneumatophore, or bladder, is the most conspicuous part of the man o' war. It is translucent, tinged blue, purple, pink, or mauve, and may be long, and rise as high as above the water. The pneumatophore functions as both a flotation device and a sail for the colony, allowing the colony to move with the prevailing wind. The gas in the pneumatophore is part carbon monoxide (0.5-13%), which is actively produced by the animal, and part atmospheric gases (nitrogen, oxygen and noble gases) that diffuse in from the surrounding air. In the event of a surface attack, the pneumatophore can be deflated, allowing the colony to temporarily submerge.