Type 901 radar

Designed by the Admiralty Surface Radar Establishment at Portsdown, the project was passed to Marconi Systems for manufacture.

As the LOPGAP programme began to focus on the Seaslug design, the 901 was re-purposed to provide aiming guidance for the missile.

Originally the antennas were mounted in front of two parabolic reflectors, one with a relatively wide beam for the gathering radar, and another with a narrower pattern for tracking.

This process took 20 – 30 seconds[8] The target-tracking and guidance beams produced were incredibly fine, being measured at 0.8° wide at 6 dB down,[9] this enabled the tracking radar to discriminate between targets as close as 20 minutes of arc or a range separation of 75 yards.

[10] Once properly gathered the missile typically remained within 35 feet of the centre of the beam[11] for the duration of the engagement.