The big four
Most warships carry four radar categories. Long-range air search (low frequency, 200+ km range, finds incoming aircraft and missiles). Surface search (X-band, 50 km range, finds ships and small craft). Navigation (10 km, mandatory for safe operation). Fire control (high-precision, narrow beam, guides each weapon). Aegis cruisers and destroyers fold all of this into a single SPY-1 or SPY-6 phased array.
Why Aegis was revolutionary
Before Aegis, a Soviet anti-ship missile attack could saturate a US warship's mechanical radars and fire-control directors. Aegis (deployed 1983) replaced them with four fixed phased-array faces and a single integrated combat system. One ship could now track 100+ targets and guide dozens of missiles simultaneously. Every modern guided-missile warship in NATO, Japan and South Korea uses Aegis or a copy of the idea.
Sea-skimming missiles and clutter
An anti-ship missile flies 5 metres above the wave tops at Mach 2 to stay below the radar horizon. Detection range against a sea-skimmer is 20-30 km — about 30 seconds of warning. Sea clutter — radar returns from waves — drowns out the target unless the radar uses Doppler filtering and ridiculous processing horsepower. The 2024 Houthi anti-ship missile attacks in the Red Sea were a real-world test of all this.
Why ships go quiet
A radiating radar is also a beacon. In wartime, ships often run EMCON (Emission Control), shutting down their radars and relying on AWACS, satellites and other ships' datalinks. The trade-off is between seeing and being seen — exactly the same problem an arcade radar player has.