Marine intervention tasks for retrieving large and heavy objects from vessels at sea is significantly important for maritime security. However, it remains a challenging task due to the lack of effective retrieval methods. Harsh open-sea conditions, unreliable GNSS due to either interruptions or deliberate spoofing by the vessels and the limitations of single robots in localizing and manipulating these objects pose significant challenges for the operations. To address these challenges, this article proposes an autonomous heterogeneous multi-robot system comprising two UAVs and a 6-DOF robot arm mounted on a USV to perform this complex task in a GNSS-denied marine environment. GNSS limitations for UAV localization are addressed using UWB beacons specially installed on the USV. Our approach involves the robot arm initially estimating the object’s position. Then the UAVs fly over the target vessel and search for the object using this information. Once object is located, a custom-designed tethered bar mechanism attached to the UAVs drags the object towards the workspace of the robot arm mounted in the USV. This work also introduces a decentralized framework to facilitate effective information sharing and collaboration among the robots. Field trials in maritime conditions demonstrate that by combining these elements, our system possesses significant potential for real-world maritime security and rescue applications. Videos for the field trails can be found at https://youtu.be/a_JzZf7QqWM