Which of the following is NOT a disadvantage of using radar in ASW operations?

The correct answer highlights that radar does have certain limitations but is not fundamentally unable to detect small targets like periscopes. In anti-submarine warfare (ASW) operations, radar systems can be effective in certain contexts, particularly for detecting periscopes as these may present a relatively larger radar cross-section compared to other small surface objects. Using specific types of radar or operating at certain frequencies can enhance the likelihood of detecting such small and partially submerged objects. This aspect is different from the other disadvantages listed, which represent inherent limitations of radar technology in the ASW context.

Additionally, the other options represent more critical disadvantages: radar is ineffective against fully submerged submarines, struggles under heavy cloud cover where signal attenuation occurs, and requires continuous surface visibility to function effectively. These factors collectively highlight the challenges faced when relying solely on radar for ASW operations. Therefore, option "C" stands out as a correct characterization of what radar can potentially achieve in specific situations within ASW, distinguishing it from the clear limitations noted in the other choices.