Issued with A.L.No.19/F

     (b)  The guns and cannon on the Spitfire IIB are fired
          pneumatically by a triple push-button on the 
          control column spade grip.   A milled finger lever
          extending from the bottom of the push button casing
          provides the means of locking the button in  the
          SAFE position, SAFE and FIRE being engraved on the
          adjacent casing.   When the lever is in the FIRE
          position a pip extends also from the top of the
          casing enabling the pilot to ascertain by feel the
          setting of the push button.

    (c)   To prevent accidental firing of the cannon on the
          ground, a safety valve is fitted in the firing
          system.  This is mounted below the undercarriage
          control unit and is coupled to the undercarriage
          locking pin cable in such a way that the cannon
          firing system is inoperative when the wheels are
          locked down.   For practice firing at the butts
          however, a finger lever on the safety valve can be
          operated to allow the use of the firing system.

    (d)   The cannons are cocked pneumatically by a cocking
          valve mounted on the right-hand side of the
          cockpit.
          
     36.  Reflector gun sight

          a)   For sighting the guns and cannon a reflector
          gun sight is mounted on a bracket (53) above the
          instrument panel.   A main switch (50) and dimmer
          switch (51) are fitted below the mounting bracket.
          The dimmer switch has three positions marked OFF,
          NIGHT and DAY.   Three spare lamps for the sight are
          stowed in holders (60) on the right hand side of
          the cockpit.
          
          b)   When the sight is used during the day the dimmer
          switch should be in the DAY position in order to
          give full illumination, and if the background of
          the target is very bright, a sun-screen (54) can
          be slid behind the windscreen by pulling on the ring
          (52) at the top of the instrument panel.   For night
          use the dimmer switch should be in the NIGHT position;
          in this positron a low-wattage lamp is brought into
          circuit and the light can be varied by rotating the
          switch knob.