I was curious after reading a book on Cold War plane development about the Soviet ideology of making increasingly powerful jets that could break Mach 3 and so on. With the advent of BVRAAM's such as the Meteor and lasers that are already being scaled down, what are the advantages to increasing the top speed or cruise speed of a fighter jet?
In the 1960, faster fighters were seen as desirable as they could outrun 1960s technology missiles to an extent (see the reports of SR-71s being fired on but never hit by SAMs). Of course, missile manufacturers saw this and developed faster missiles and longer-range radars to negate this advantage. And as it is much easier to make a missile faster than it is to make a large aircraft faster, that's an arms race the airplane manufacturers always lose.
While high speed allows you to outrun missiles, it also reduces maneuverability: at Mach 3, a constant-G turn will be much larger than turning at the same G level at Mach 1.
what are the advantages to increasing the top speed or cruise speed of a fighter jet?
It's often thought that speed is used to avoid attack, but that is rarely successful. It's far easier to make a faster fighter or missile than a faster, say, bomber. This has gone back and forth over the years, see schellbomber for instance, but invariably the defense had the easier job - especially once they had radar and interceptions were arranged in front.
The real reason speed is useful, especially in the 50s and 60s, was that the interception process itself was manual. So if the guy on the ground has a radar with a 200 mile range against your bomber and you're flying Mach 3, you're going to be overhead in 5 minutes and disappear in 10. That leaves very little time for the operator to arrange an interception. If the interceptor starts on the ground, it's not going to happen, period.
That, of course, changed with the introduction of SAMs. Now the only need for the operator is to figure out roughly where you're going and alert the closest SAMs along that line. Five minutes is lots of time for them to get ready.
There is, of course, the advantage of confusing the defense network as a whole; Moscow is maybe 15 minutes from the coast in a B-70, and that doesn't leave lots of time to get prepared. But in the era of ICBMs, that too is enough time.
And so speed sort of went away and was replaced by low-level flying, jammers, SRAM and so on. If you're going to blast your way through the defenses with SRAM, doing so quickly doesn't really offer much of an advantage, the missile is going much faster than you ever will.
But all that is old is new again, and speed is once again showing some advantages. In the case of the F-22 the idea is simply to have enough performance that the combination of altitude, speed and stealth/detection range keep you out of the lethal volume of the missiles below you. So against something like the S300, the missile has excellent performance and can shoot you down, but it will only see you at short ranges and you're way up in the air, so by the time they get a tracking solution you're already out of range. That's significantly more difficult to pull off if you're flying 30% slower.