What should accompany the Requesting Participant's Form 1 to verify a vessel's nationality?

The Requesting Participant's Form 1 must be accompanied by the reasonable grounds for suspicion as this provides the necessary basis for conducting a boarding. Reasonable grounds for suspicion serve as the justification that the vessel may be engaging in illegal activities or may not be flying its flag legitimately. This documentation is essential because it underscores the legitimacy of the request to verify the vessel's nationality and ensures that responses to such requests are founded on credible concerns. This component plays a crucial role in maintaining lawful maritime operations and preventing unlawful activities on the high seas.

Other elements such as previous boardings, crew member lists, or cargo documentation are helpful in broader contexts of maritime operations but do not specifically fulfill the primary requirement of establishing the justification necessary for validating a vessel's nationality during the boarding process.