Small drifting objects can be a big threat to surface ships, especially when the objects are explosion hazards like sea mines that have become detached from their moorings. Timely detection of such objects is crucial in order to be able to perform adequate evasive manoeuvres. Due to the uncontrolled nature of drifting mines, permanent scanning of the horizon is required. On the other hand, these continual search activities should not have a significant operational impact on the ship’s mission. Therefore, automatic detection by time-interleaved use of existing surface radar and electro-optical systems from the ship’s mast seems attractive. However, what are the actual chances of such systems to detect a largely submerged sea mine at sufficient distance for representative weather conditions? This paper reports on the effectiveness of state-of-the-art surface radar and electro-optical systems as part of a ship’s organic MCM capability, based on literature study, theoretical considerations and sea trial results. Other possible approaches are discussed.