Argo Clock Mark IV
Principles of Operation
Courtesy of Dr. John Brooks.
1. Underneath the bearing dial, a dumaresq-type linkages modelled the courses and speeds of own and enemy ships. Both courses were expressed relative to the line-of-sight from own ship to enemy. Own course was represented as the angle between own heading and the line-of-sight i.e. as the target bearing angle. Enemy course was represented as the angle from the line-of-sight to the enemy course — in RN terminology, by the 'inclination'. In what follows, I assume the enemy course was steady.
2. The dumaresq mechanism resolved own and enemy ship speed vectors into components along and across the line-of-sight. It then subtracted these components to obtain the components of the velocity of the enemy relative to own ship, both along and across (at right angle to) the line-of sight. The "speed-along" gave the relative speed of the enemy towards or away from own ship i.e. the range-rate.
3. The 'speed-across', when divided by range with a dividing mechanism, gave the rate of change of enemy compass-bearing and the rate of change of inclination. When own course was steady, this was also the rate of change of target-bearing.
4. Assuming the enemy-bearing and inclination angles are correct, the mechanism generates range-rate and bearing-rate, correct from instant to instant. Thus, if the two rates are applied to integrators, those integrators correctly generate change-of-range and change-of-bearing. Thus, if it is started with correct values of range and bearing, the clock can keep the range and bearing as it changes.
5. By applying the change-of-enemy-bearing and change-of-inclination to the dumaresq mechanism and the correct range to the dividing mechanism, the clock was able to continue generating correct range-rate and bearing-rate. Thus the loop was closed and operation ws automatic.
6. However, with the Mark IV, this was only true while own course was steady. It had no input for change of own course, so it could not keep automatically the change in enemy-bearing when own ship changed course. Hence the STEADY/TURNING lever, which disconnected the bearing clock from the bearing-dial so that enemy bearings, could be set manually.
7. However, the bearing clock remained connected to the enemy linkage of the dumaresq so that the clock could keep the inclination, even in a turn. Thus, provided the enemy-bearing was set correctly by hand, the clock kept range exactly, even in a turn.