For its lethal drone programme, the United States relies heavily on assistance from many States, including European States. Article 16 of the Draft Articles on Responsibility of States for Internationally Wrongful Acts (Draft Articles) sets out the conditions for a State’s legal responsibility for its assistance. It reads:
A State which aids or assists another State in the commission of an internationally wrongful act by the latter is internationally responsible for doing so if:
(a) that State does so with knowledge of the circumstances of the internationally wrongful act; and
(b) the act would be internationally wrongful if committed by that State.
The commentaries accompanying the Draft Articles explain that three requirements must be met for Article 16 to be applicable (p. 65-67). First, the assisting State must have had knowledge of the circumstances of the internationally wrongful act of the recipient State.
Secondly, the assisting State must give its assistance with the intention that the act will be committed and the act must actually be committed. There is no requirement that the aid or assistance should have been essential to the performance of the internationally wrongful act; it is sufficient if it contributed significantly to it.
Thirdly, the completed act must be such that it would have been wrongful had it been committed by the assisting State itself. The commentary highlights that State practice supports assigning international responsibility to a State which deliberately participates in the internationally wrongful conduct of another through the provision of aid or assistance, in circumstances where the obligation breached applies equally to the assisting State.
Under Article 16, the responsibility of assisting State is limited to its own act; it is not responsible for the act of the recipient State. Consequently, the assisting State is not necessarily to be held to indemnify the victim(s) for all the consequences of the act, but only for those which flow from its own conduct.
 There is debate about the legal status of the Draft Articles; some consider them as soft law whereas others assign them the status of customary law.