573,621. Wireless systems ; thermionic relay circuits. WALTON, G. W. Jan. 11, 1941, No. 407. [Class 40 (v)] [Also in Group XXI] A system tor detonating the explosive charge of a projectile, torpedo, bomb or like missile comprises in combination (a) means in the missile or at a remote control station for generating and propagating influence such as electromagnetic waves, (b) apparatus on the missile responsive to the influence and to one or more other effects, such as electrical capacity or inductance, fluid disturbance, or inertia and centrifugal forces acting in the vicinity of the target, and (3) a detonating compound fired by the said apparatus in response to the influence or other effect. The means described for actuating the fuze in proximity to the target include means controlled by entry of the shell into'(1) a radio beam from the remote station acting directly or by reflection from target, (2) a space close to a target in which there is a variable electric capacity effect, or (3) the slipstream of the target which either causes precession of the shell to trip the fuze by centrifugal force or builds up a difference of pressure in the shell to actuate the fuze. Fig. 1 shows a safe inertia-actuated percussion fuze adjusted to great sensitivity and tired by electric contacts 14, 21 by a member 9 supported by toggles 8 engaging upper and lower grooves in the member 9 and spring members 7. The source of electric energy for firing is a condenser 23 charged, just prior to discharge of the projectile, from a source of electric potential such as a generator or highvoltage rectifier, by making contacts at 1 and 21. The condenser discharges across a spark gap 27 situated in a fulminate detonator 28. The condenser may be replaced by an electric battery or generator for heating a filament in the detonator. Safety until the projectile is in flight is obtained by spring pawls 16 on a member 9 until the pawls swing out by centrifugal force due to projectile spin. The pawls cannot be released otherwise than by spin and the member 9 is firmly pressed by inertia against the member 18 until acceleration ceases. Sensitivity is adjusted by a screw on the member 18 to bring the toggles 8 nearer to the dead-centre position or by attaching weights to the free ends of the springs 7. In addition to inertia actuation, electromagnetic actuation is effected by the reception of electromagnetic waves by a wireless receiver in the projectile, including a tuning coil 32, Fig. 2, crystalrectifier 30 and trimming condenser 40. The rectified current passes to a solenoid 36 clad with iron plates 37, 38 and a steel cylinder 5 and the soft-iron member 9 is drawn into the coil 36 when the current flows. The stationary trimming condenser 40, Fig. 1, is formed of part cylinders adjusted by a screw-driver inserted through an aperture 42. The parts are arranged as in Fig. 2 to receive ultra-short electromagnetic waves the projectile 43 providing a single pole antenna connected to the coil 32. The fuze is actuated by the projectile entering a short-wave beam emitted from a remote station and directed at the target. The beam may serve to explode shells fired from a number of guns and the explosion may also be controlled by time or by proximity of the projectile to the target as by radio echo therefrom. The timing device is at the remote station and not within the projectile and can be adjusted during flight of the projectile. It comprises an electric commutator device to provide an adjustable time interval up to 20 secs. between the closing of a circuit for projectile discharge and the closing of another circuit for switching on the beam. To actuate the fuze by the beam reflected from the target, the arrangement of Fig. 2 is tuned to a wavelength slightly shorter than the beam and the increased capacity between the parts 3, 1, due to proximity of the target, brings the projectile into tune with the beam and actuates the fuze. The wave-length of the beam may be increased while the projectile is in flight. The control beam and station described in Specification 539,224 can be employed for the beam control of the projectile or torpedo and the fuze may be actuated by the steering control producing a turn of the missile in the vicinity of the target, as described in the specification referred to. When the projectile has a source of electric energy such as a generator operated by the spin of the projectile, the electric device may be made more sensitive by including in the projectile a thermionic valve such as an oscillator valve 79 in a circuit as shown in Fig. 10, using a wave-length up to 50 metres which will actuate the fuze if the circuit of Fig. 2 is detuned so that proximity of the target within 25 metres brings the circuit into tune with the oscillator 79. Fig. 11 also shows a circuit diagram for an arrangement independent of beam control for " proximity " actuation comprising a combined short-wave wireless transmitter X and receiver Y separated by a screen 86, the parts being mounted in the missile and operating from the fuze by radio echo from the target. The parts include an oscillator valve 79 and aerial system 43 in the transmitter and a rectifying valve 89 and thermionic or gas relay 92 for firing the detonator 94. The sensitive fuze of Fig. 1 may be so adjusted that it is tripped by the precessional torque on a missile entering the slip stream of the airscrew of the target aeroplane or by air pressure built up in the compartment containing the member 18 by air from outside entering a passage 98 past a non-return valve 99. The built-up pressure during discharge from the gun is prevented by inertia action of a weight 100 pressing on the valve. The invention is also applicable to torpedoes and bombs dropped from aircraft.