In restricted visibility a power-driven vessel under way gives which sound signal?

In restricted visibility, a power-driven vessel under way is required to sound one prolonged blast followed by two short blasts at intervals of not more than two minutes. This signal indicates the vessel's presence and helps other vessels determine its position and heading. The prolonged blast lasts about four to six seconds, while each short blast lasts about one second. Additionally, vessels may also sound the signal to indicate their intent to maneuver or when they are overtaking another vessel.