Underwater vehicle manufacturer Bluefin Robotics, which has its headquarters in Quincy, Massachusetts, did not disclose how much it paid for Edinburgh-based SeeByte.
The businesses have worked together on projects for more than five years.
According to its 2012 accounts, SeeByte - a Heriot-Watt University spin-out - made £1.4 million profit on turnover of £4.4m.
SeeByte, which has clients in the military and oil and gas sectors, said all its staff are being retained.
Bluefin is owned by the not-for-profit science and technology charitable trust Battelle.