Related Rule
Ecuador
Practice Relating to Rule 20. Advance Warning
Ecuador’s Naval Manual (1989) states:
When circumstances permit, advance warning should be given of attacks that might endanger noncombatants in the vicinity. Such warnings are not required, however, if mission accomplishment requires the element of surprise or the security of the attacking forces would be otherwise compromised. 
Ecuador, Aspectos Importantes del Derecho Internacional Marítimo que Deben Tener Presente los Comandantes de los Buques, Academia de Guerra Naval, 1989, § 11.2; see also § 8.5.2.
The manual specifies that: “Warnings may be general rather than specific lest the bombarding force or the success of its mission be placed in jeopardy.” 
Ecuador, Aspectos Importantes del Derecho Internacional Marítimo que Deben Tener Presente los Comandantes de los Buques, Academia de Guerra Naval, 1989, § 8.5.2.