Submarine liquid compass

Bowl- Aluminium, painted grey, filler plug at side. At base of bowl are fitted two expansion chambers, a glass aperture to permit projection of card image onto screen, three legs and two frames to take corretor magnet strips. Inside of bowl fitted with inner skin (black) and a fitting on aft side permits air bubbles to be removed by tilting bowl and allowing them to run up between the two skins. A metal lubber pointer is fitted which can be moved against a graduated scale by a knob working through a gland on the fore side of bowl. Mounted in aluminium gimbal ring 10.75" (27.3cm) in diameter.
Card- Metal card with heavy float. Markings are perforations graduated to 360 degs.
Needle- Four flat needles in metal cases mounted below card.