A control system for controlling a projectile, the control system comprising: a plurality of transmitters (210a, 210b, 210c, 210d), wherein each transmitter of the plurality of transmitters (210a, 210b, 210c, 210d) is arranged to transmit an electromagnetic wave (21a, 21b, 21c, 21d) from a transmission position; a projectile comprising; a receiver within the projectile, the receiver being arranged to receive a plurality of electromagnetic waves (21a, 21b, 21c, 21d) transmitted from the plurality of transmitters (210a, 210b, 210c, 210d); and a controller within the projectile, the controller being arranged to: determine at least one of a position, a velocity or an acceleration of the projectile from transmission positions of the plurality of transmitters and Doppler measurements derived from the received plurality of electromagnetic waves (21a, 21b, 21c, 21d); and generate a control signal for performing an action with the projectile depending on the determined at least one of position, velocity or acceleration of the projectile; the control system being characterized by a locator, external to the projectile and transmitters (210a, 210b, 210c, 210d), the locator comprising a transmission position determiner to detect at least one of the plurality of transmitters (210a, 210b, 210c, 210d), determine at least one transmission position of the detected at least one of the plurality of transmitters (210a, 210b, 210c, 210d), encode data for identifying each of the detected at least one transmitter and its determined transmission position on an electromagnetic wave and transmit that electromagnetic wave to the projectile after firing, wherein the projectile is arranged to receive, from the locator, the electromagnetic wave, and retrieve the determined at least one transmission position from the data by decoding data encoded in the received electromagnetic wave. a plurality of transmitters (210a, 210b, 210c, 210d), wherein each transmitter of the plurality of transmitters (210a, 210b, 210c, 210d) is arranged to transmit an electromagnetic wave (21a, 21b, 21c, 21d) from a transmission position; a projectile comprising; a receiver within the projectile, the receiver being arranged to receive a plurality of electromagnetic waves (21a, 21b, 21c, 21d) transmitted from the plurality of transmitters (210a, 210b, 210c, 210d); and a controller within the projectile, the controller being arranged to: determine at least one of a position, a velocity or an acceleration of the projectile from transmission positions of the plurality of transmitters and Doppler measurements derived from the received plurality of electromagnetic waves (21a, 21b, 21c, 21d); and generate a control signal for performing an action with the projectile depending on the determined at least one of position, velocity or acceleration of the projectile; the control system being characterized by a locator, external to the projectile and transmitters (210a, 210b, 210c, 210d), the locator comprising a transmission position determiner to detect at least one of the plurality of transmitters (210a, 210b, 210c, 210d), determine at least one transmission position of the detected at least one of the plurality of transmitters (210a, 210b, 210c, 210d), encode data for identifying each of the detected at least one transmitter and its determined transmission position on an electromagnetic wave and transmit that electromagnetic wave to the projectile after firing, wherein the projectile is arranged to receive, from the locator, the electromagnetic wave, and retrieve the determined at least one transmission position from the data by decoding data encoded in the received electromagnetic wave.