The modification is valued at $14.5m and will require the company to exercise the fourth-year option under an existing contract to provide Ku satellite bandwidth and support services for the US Marine Corps' Tactical Satellite Communications Network.
Comtech is providing commercial satellite services to various terminals in order to extend the Marine Corps Enterprise Network for deployed users.
Commenting on the deal, Comtech Telecommunications president and chief executive officer Fred Kornberg said: "The decision by DISA to exercise the fourth-year option demonstrates that the Comtech team continues to provide a valued service to the US Marine Corps.
"Comtech is committed to providing its customers with cost-effective, reliable and secure communications solutions that enable them to successfully complete their missions."
The customer has funded $73m on this contract to date, and the fourth option year will cover the period from 1 August 2017 through to 31 July 2018.
The order was issued under the joint DISA / US General Services Administration (GSA) Future Commercial SATCOM Acquisition programme. DISA and GSA are managing this procurement via the $2.6bn Custom SATCOM Solutions (CS2) contract vehicle.
Comtech Telecommunications’ Command & Control Technologies group is part of Comtech's Government Solutions segment and provides mission-critical, highly mobile command, control, communications, computers, intelligence, surveillance and reconnaissance (C4ISR) solutions.