Related Rule
United States of America
Practice Relating to Rule 79. Weapons Primarily Injuring by Non-Detectable Fragments
The US Air Force Pamphlet (1976) states: “Usage and practice has also determined that it is per se illegal to use projectiles filled with glass or other materials inherently difficult to detect medically.” 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 6-3(b)(2).
The US Air Force Commander’s Handbook (1980) states: “Using clear glass as the injuring mechanism in an explosive projectile or bomb is prohibited, since glass is difficult for surgeons to detect in a wound and impedes treatment.” 
United States, Air Force Pamphlet 110-34, Commander’s Handbook on the Law of Armed Conflict, Judge Advocate General, US Department of the Air Force, 25 July 1980, § 6-2(a)(2).
The US Instructor’s Guide (1985) states that the principle of unnecessary suffering “outlawed the use of … projectiles filled with glass”. 
United States, Instructor’s Guide – The Law of War, Headquarters Department of the Army, Washington, April 1985, p. 7.
The US Naval Handbook (1995) provides: “Using materials that are difficult to detect or undetectable by field x-ray equipment, such as glass or clear plastic, as the injuring mechanism in military ammunition is prohibited, since they unnecessarily inhibit the treatment of wounds.” 
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), § 9.1.1.
The US Naval Handbook (2007) states:
[U]sing materials that are difficult to detect or undetectable by field x-ray equipment, such as glass or clear plastic, as the injuring mechanism in military ammunition is prohibited, since they unnecessarily inhibit the treatment of wounds. Use of such materials as incidental components in ammunition, e.g., as wadding or packing, is not prohibited. 
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, § 9.1.1.
In 1979, in a legal review of the Maverick Alternate Warhead, the US Department of the Air Force stated:
It is generally accepted … that … only weapons designed to injure through non detectable fragments would be prohibited. Incidental effects arising from the use of a few plastic parts in a munition would still be considered lawful. 
United States, Air Force, Judge Advocate General, Legal Review of Maverick Alternate Warhead, (AGM-65E), 4 January 1979, § 3.
Upon ratification of the 1980 Convention on Certain Conventional Weapons, the United States declared:
With reference to the scope of application defined in article 1 of the Convention, that the United States will apply the provisions of the Convention, Protocol I, and Protocol II to all armed conflicts referred to in articles 2 and 3 common to the Geneva Conventions for the Protection of War Victims of August 12, 1949 [international and non-international armed conflicts]. 
United States, Declaration made upon ratification of the Convention on Certain Conventional Weapons, 24 March 1995.