Which level of investigation is required for someone to gain eligibility to access Top Secret information?

The correct answer is that a Tier 5 investigation is required for someone to gain eligibility to access Top Secret information. A Tier 5 investigation is the most comprehensive level of security clearance screening, which includes in-depth background checks that investigate an individual's personal and professional history, as well as their character and associations. This thorough examination is necessary for protecting sensitive national security information, as it ensures that those granted Top Secret access have been evaluated for potential vulnerabilities or risks that could compromise security interests.

In comparison, Tier 2, Tier 3, and Tier 4 investigations are appropriate for lower levels of clearance, such as Confidential and Secret, which do not require the same level of scrutiny as the Tier 5 investigation. Each tier corresponds to the sensitivity of the information accessed, making it vital to use the correct investigation approach for different clearance levels to maintain national security.