In NTDS, the computer carrying the tactical picture also carried the what-if software, which was relatively simple. In Aegis, the computer carrying the tactical picture works with a separate command and decision (C&D) computer, which applies tactical doctrine (embodied in software controlled on board the ship) to the tactical picture. Tactical doctrine may include filters to protect the picture-keeping computer from being swamped by tracking, for example, slow-flying seabirds. A third computer creates tactical pictures for training purposes, injecting them into the other two computers. In effect, the third computer showed that the Aegis system might make use of a picture, or of parts of a picture, which did not originate in a ship’s own radar. That later became significant when Aegis ships linked their computers into a Cooperative Engagement Capability (CEC) network.

The Aegis developers were lucky that computers and microelectronics in general were developing so rapidly. When they began work in 1963 (on a replacement for the canceled Typhon system, which first embraced the electronically scanned missile control radar idea), they could look forward to a generation of reliable computers much faster than those used in NTDS. It probably helped that the considerable problems of NTDS lay in the future – problems associated with insufficient computer speed and memory. Within a few years what would become the Aegis project had fastened on flat electronically scanned radar antennas as the technology of the future. The radar selected for Aegis was RCA’s (now Lockheed Martin’s) SPY-1. It has become the signature feature of the system.

SPY-1 was not quite precise enough to guide a defensive missile all the way to the target. The developers chose a combination approach. As in its earlier incarnations, a Standard fired by an Aegis system ultimately guides itself by homing on reflected radar radiation. However, it does so only in the final moments of flight. Until that point, the missile flies a course dictated by the system computer, which periodically updates its autopilot. This is a kind of command guidance (an abandoned earlier technique), but because it is imposed only periodically, it does not tie up a director. The number of missiles the system can control is limited mainly by system computer capacity. The illumination at the end, once the missile has been guided into a homing “basket,” comes from a director controlled by the system computer. Illuminators are time-shared. Aegis ships typically have three or four such illuminators – which are enough for a lot more than three or four channels.

Initially, the only difference between a Standard Missile fired by an earlier-generation missile ship and a Standard fired by an Aegis ship was that the latter had an autopilot that could be controlled in flight from the firing ship, for the intermittent command guidance employed by the Aegis system. That made an enormous difference because the controlling computer on the ship could fly the missile along a more energy-efficient path (rather than having the missile pursue the target directly, as in the past). Typically the better path was up-and-over, the missile benefitting from gravity as it dove after its fuel had been burned up. This difference alone radically increased missile range: from 17.5 nautical miles (nm) for Standard in the earlier Tartar system to 40 nm in the early Aegis ships (range increased further once the missile had a better motor).

Aegis had another, subtler, advantage over earlier systems. It was not the first U.S. Navy anti-air missile system to employ digital computers, but it went much further in using software rather than hardware for control. In earlier systems, nearly all changes required massive rewiring and new hardware. When Ticonderoga encountered teething problems, they were quickly solved with software patches – much as is now familiar in personal computers. Conversely, it was relatively easy to transfer Aegis software to more powerful computers, when they became available.

To work as planned, Aegis needed a much more precise – much cleaner – tactical picture than the earlier NTDS. The Aegis developers realized that the tactical picture used for missile guidance should also be the one used by the command, replacing the usual NTDS system entirely. That turned out to be a vital choice. The picture was so clean and so crisp that commanders found it extremely useful. The developers displayed it not on the small screens of the past but on enormous projection screens, something not seen before. “Aegis” cruisers were soon used as command ships, because force commanders wanted to be where the best information was. For many, Aegis was the first time they saw the sort of computer-generated pictures later commonplace on personal computers. For years after the Ticonderoga entered service, the demand was for ‘Aegis’ in other contexts – often meaning that crisp picture of what was happening. The clarity of the picture came both from modern computer technology and from the way in which the command and decision processor linked individual radar plots (detections) into meaningful tracks.

The clear tactical pictures turned out to be more important than the Standard Missiles, because for the first time those on board ships were able to disentangle particularly complicated situations. That was first demonstrated in 1985, when an Aegis cruiser controlled the F-14s that intercepted an airliner carrying terrorists above the Mediterranean, in a night sky full of other aircraft.