Related Rule
United States of America
Practice Relating to Rule 8. Definition of Military Objectives
Section E. Lines and means of communication
The US Air Force Pamphlet (1976) states:
Controversy exists over whether, and the circumstances under which, other objects, such as civilian transportation and communications systems, dams and dikes can be classified properly as military objectives … A key factor in classification of objects as military objectives is whether they make an effective contribution to an adversary’s military action so that their capture, destruction or neutralization offers a definite military advantage in the circumstances ruling at the time. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 5-3(b)(2).
The US Naval Handbook (1995) considers communications and command and control facilities, as well as “lines of communication and other objects used to conduct or support military operations”, as proper targets for naval attack. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 8.1.1.
The US Naval Handbook (2007) states:
Proper objects of attack include, but are not limited to, such military objectives as … lines of communication and other objects used to conduct or support military operations … [and] communications and command and control facilities. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-12.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Homeland Security, US Coast Guard, July 2007, § 8.2.5.
During the Korean War, the United States reportedly attacked communication centres in North Korea. 
Robert F. Futrell, The United States Air Force in Korea 1950–1953, Office of Air Force History, United States Air Force, Washington, D.C., Revised edition, 1983, p. 516.
In 1950, the US Secretary of State stated: “The air activity of the United Nations forces in Korea has been, and is, directed solely at military targets of the invader. These targets [include] … communications lines.” 
United States, Statement by Dean Acheson, Secretary of State, 6 September 1950, reprinted in Marjorie Whiteman, Digest of International Law, Vol. 10, Department of State Publication 8367, Washington, D.C., 1968, p. 140.
In 1991, in reports submitted to the UN Security Council on operations in the Gulf War, the United States included command and control centres among Iraq’s military targets. 
United States, Letter dated 22 January 1991 to the President of the UN Security Council, UN Doc. S/22130, 22 January 1991, p. 1; Letter dated 8 February 1991 to the President of the UN Security Council, UN Doc. S/22216, 13 February 1991, p. 1.
In 1991, during a news briefing concerning the Gulf War, the US Secretary of Defense stated that “command and control [and] communications facilities” were considered military targets and had been attacked. 
United States, News Briefing by the US Secretary of Defense and the Chairman of the Joint Chiefs of Staff, Washington, 23 January 1991, annexed to Letter dated 25 January 1991 to the President of the UN Security Council, UN Doc. S/22168, 29 January 1991, p. 3.
In 1992, in its final report to Congress on the conduct of the Gulf War, the US Department of Defense stated that Iraq’s leadership command facilities, its telecommunications and command, control and communication nodes had been included among the 12 target sets for the coalition’s attacks. 
United States, Department of Defense, Final Report to Congress on the Conduct of the Persian Gulf War, 10 April 1992, Chapter VI, The Air Campaign, pp. 95–96.
The report specified that:
To challenge [Saddam Hussein’s] C3 [command, control and communication], the Coalition bombed microwave relay towers, telephone exchanges, switching rooms, fiber optic nodes, and bridges that carried coaxial communications cables … More than half of Iraq’s military landline communications passed through major switching facilities in Baghdad. Civil TV and radio facilities could be used easily for C3 backup for military purposes. The Saddam Hussein regime also controlled TV and radio and used them as the principal media for Iraqi propaganda. Thus, these installations were also struck. 
United States, Department of Defense, Final Report to Congress on the Conduct of the Persian Gulf War, 10 April 1992, Chapter VI, The Air Campaign, p. 96; see also James P. Coyne, Plan of Attack, Air Force Magazine, April 1992, pp. 40–42.
In the same report, the Department of Defense stated: “Microwave towers for everyday, peacetime civilian communications can constitute a vital part of a military command and control (C2) system … Attack of all segments of the Iraqi communications system was essential to destruction of Iraqi military C2.” 
United States, Department of Defense, Final Report to Congress on the Conduct of the Persian Gulf War, 10 April 1992, Appendix O, The Role of the Law of War, ILM, Vol. 31, 1992, p. 623.