The cause of the crash of the AH-64 Apache helicopter, some 25 miles (40 km) southeast of Houston, was not known.
The two men who were killed were pilots from a helicopter battalion at Ellington Field in Houston, Reuters reported.
The names of those killed have not been released.
The crash did not affect navigation in the Houston Ship Channel, which links the busiest US petrochemical port to the Gulf of Mexico, the Houston Pilots Association said.