The correct answer is B) They provide increased maneuverability at low ship speeds. Transverse bow and stern tunnel thrusters are primarily used to enhance a ship's maneuverability, especially at low speeds. These thrusters can generate sideways thrust, allowing the vessel to move laterally without changing its heading. This improved low-speed maneuverability is particularly useful for docking, undocking, and tight maneuvering in restricted waterways. The other options are incorrect because: A) Thrusters are not the primary source of reverse thrust, which is typically provided by the main propulsion system. C) Thrusters do not significantly increase overall forward thrust compared to the main propulsion. D) Thrusters are more effective at low speeds, as their influence diminishes at higher speeds when hydrodynamic forces become more dominant.