MIL-T-16420K, MILITARY SPECIFICATION: TUBE, COPPER-NICKEL ALLOY, SEAMLESS AND WELDED (COPPER ALLOY NUMBERS 715 AND 706) (14 APR 1978)., This specification covers two compositions of round copper-nickel alloy tube for basic piping systems on surface ships and submarines as referenced in MIL-STD-777 and MIL-STD-438. Tube and pipe sizes permit the use of Naval fittings designed for brazed or welded connections.