Chief hospital corpsman James Buchanan, assigned to Naval Mobile Construction Battalion 17, tests drinking water in one of the six "water bulls" which contain 300 gallons of drinking water for the battalion while in the field. Water must be tested several times a day to ensure the purity of water for the Seabees. NMCB-17 Seabees are taking part in the field exercise Operation Bearing Duel. (U.S. Navy Photo/mass communication specialist 2nd Class Kenneth W. Robinson)