foreplane

A foreplane, in submarine terminology, is a forward-mounted horizontal control surface used to manage the pitch and depth of the vessel. Also commonly called bow planes, foreplanes are part of the submarine’s diving controls and work in tandem with stern planes and ballast systems to achieve controlled ascent, descent, and trimming of the hull.

Foreplanes are typically installed on the forward portion of the hull, often arranged in pairs on either side of the bow. They can be fixed or movable, with many designs using hinged or all-moving surfaces that allow precise adjustment of the bow’s attitude in the water. By angling the foreplanes downward, the submarine’s bow tends to dive; angling them upward lifts the bow and helps raise depth or initiate surfacing. The foreplanes thus serve as the primary means of initiating submergence and controlling initial pitch, with stern planes providing additional depth control and stability.

Historically, foreplanes became standard on many 20th-century submarines as a reliable mechanism for depth control. They were widely employed by various navies during the World War II era and continued to be used in later submarine classes, although modern designs have integrated their control surfaces more deeply into hull forms and electronic control systems. The specific arrangement and number of foreplanes vary by class and era, reflecting advances in hydrodynamics and automation.

In practice, foreplanes are distinct from stern diving planes and other vertical fins; all such control surfaces work together under the submarine’s trim and ballast management systems to maintain depth, attitude, and maneuverability. The term can be encountered as bow planes in some classifications, but the underlying function remains consistent: forward hydroplanes used to control pitch and depth of the submarine.