An Inertial Navigation System, INS, comprising: a) an INS unit for providing navigation during a dynamic state which: i. comprises an IMU which comprises a set of at least three gyros and at least three accelerometers, all mounted on a rotatable stage; and ii. said INS unit is configured to run an INS algorithm for taking measurements from said gyros and said accelerometers during a mission, and calculating a navigation solution based on said measurements; b) a true north finding unit, which: i. comprises one or more from said IMU gyros and one or more from said IMU accelerometers, said one or more IMU gyros and accelerometers are common to said INS unit and to said true north finding unit; and ii. said true north finding unit is configured to run a true north finding algorithm which utilizes measurements from said common gyros and accelerometers during a stationary state for determining initial conditions, during said stationary state the stage is positioned successively in at least two separate stationary orientations, said north finding algorithm determines a true north solution which is provided to the INS unit for initializing its said INS algorithm, wherein said INS algorithm further looks periodically for said stationary state in order to reactivate during this state the north finding algorithm, which in turn updates the INS algorithm by performing an alignment update. a) an INS unit for providing navigation during a dynamic state which: i. comprises an IMU which comprises a set of at least three gyros and at least three accelerometers, all mounted on a rotatable stage; and ii. said INS unit is configured to run an INS algorithm for taking measurements from said gyros and said accelerometers during a mission, and calculating a navigation solution based on said measurements; i. comprises an IMU which comprises a set of at least three gyros and at least three accelerometers, all mounted on a rotatable stage; and ii. said INS unit is configured to run an INS algorithm for taking measurements from said gyros and said accelerometers during a mission, and calculating a navigation solution based on said measurements; b) a true north finding unit, which: i. comprises one or more from said IMU gyros and one or more from said IMU accelerometers, said one or more IMU gyros and accelerometers are common to said INS unit and to said true north finding unit; and ii. said true north finding unit is configured to run a true north finding algorithm which utilizes measurements from said common gyros and accelerometers during a stationary state for determining initial conditions, during said stationary state the stage is positioned successively in at least two separate stationary orientations, said north finding algorithm determines a true north solution which is provided to the INS unit for initializing its said INS algorithm, wherein said INS algorithm further looks periodically for said stationary state in order to reactivate during this state the north finding algorithm, which in turn updates the INS algorithm by performing an alignment update. i. comprises one or more from said IMU gyros and one or more from said IMU accelerometers, said one or more IMU gyros and accelerometers are common to said INS unit and to said true north finding unit; and ii. said true north finding unit is configured to run a true north finding algorithm which utilizes measurements from said common gyros and accelerometers during a stationary state for determining initial conditions, during said stationary state the stage is positioned successively in at least two separate stationary orientations, said north finding algorithm determines a true north solution which is provided to the INS unit for initializing its said INS algorithm, wherein said INS algorithm further looks periodically for said stationary state in order to reactivate during this state the north finding algorithm, which in turn updates the INS algorithm by performing an alignment update.