Rocket interceptor II, with +5 to range, still gets a -15% penalty to mission efficiency due to lack of range when trying to defend Berlin.
With +5 to Range and +5 to Reliability, they still have 50% reliability. They use 1 more aluminum than Jet I. They cost 18, versus the 30 cost for Jet I and the 28 cost for 1944 light fighter. To research Rocket Interceptor II, you need to push past 1944 rockets to 1945 rockets, while jets require 1944 rockets, jet engines, then the jet tech itself.
Rocket Interceptor II (base model) does have an air attack of 56, placing it well ahead of Jet I, 1944 light fighter, and slightly ahead of 1944 Heavy Fighter. It is much faster than 1944 Light Fighter and Heavy Fighter, and slightly faster than Jet I. Never forget that speed also affects air to air combat, not just agility.
Let's test their performance against unescorted bombers and escorted bombers. We will test Rocket Interceptor IIs, Jet I, 1944 Heavy and Light Fighters, versus unescorted 1944 Heavy Bombers and 1944 Light Fighters as escorts. I will use 500 STRs (for a total IC cost of 32,000) versus an equal IC cost of rockets (1777), jets (1066), light fighters (1142), and heavy fighters (1000).
For this test, since we aren't trying to measure bomber performance, we will use "final form" fighters. That is, the fighters will have all upgrades I think they should have regardless of the XP cost. The fighters will get their appropriate design company: light fighters get the light fighter one, the heavy fighters get theirs. No design company affects rockets or jets. The bombers and escorts get 100% of the Strategic Destruction tree filled out, the defenders get 100% of the Operational Integrity. We will have the bombers fly from Britain to the Ruhr valley, with the Germans defending. Both sides get maximum RADAR to aid in detection (these are all late war techs, so all these goodies make sense).
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Rocket Interceptor IIs get +5 engine, +5 range, and +5 reliability. I don't increase their guns, because their reliability starts out so poor that if it gets much lower, they will just catch on fire upon take off.
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The Jets get +5 engine, +1 guns, +4 range, and +5 reliability.
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The light fighters get +5 engines, +1 guns, +1 range, +3 reliability
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The heavy fighters get +5 engines, +5 guns, and +3 reliability (remember, the medium aircraft designer gives them increased reliability, so I don't need as much on the plane if I boost guns all the way.)
From these screnshots, it's clear that jets are catching up to rocket interceptors in terms of speed, are better at agility and range. Heavy fighters have far better air attack than the rockets, but lose in terms of speed and agility. The light fighters dominate agility, but don't have the firepower or speed of the rockets.
Against unescorted bombers, for 30 days, here's what it looks like with rockets:
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No buildings lost, 232 rockets dead from both enemy fire and accidents (4176 IC) versus 121 STRs dead to enemy fire (no AA in the state, 7744 IC dead). Not bad at all. Note, though, that rockets can only run interception. They cannot provide air superiority at all.
Against jets:
View attachment 395214
0.5 buildings were hit by the STRs. (That's practically nothing, though.) 101 jets lost to all causes (3030 IC) versus 63 STRs lost to enemy fire (4032). Jets win against unescorted bombers, but they are far less IC efficient than the rockets.
Against Heavy Fighters:
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1.1 buildings were damaged by the bombers (again, this is practically nothing). Heavy fighters lost 84 planes to all causes (2688 IC), while the STRs lost 115 (7360). Despite some minor bomb damage, the heavy fighters performed really well, beating rockets and jets.
Against Light Fighters:
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1.0 buildings damaged (again, that's practically nothing). The light fighters lost 94 planes to all causes (2632 IC) versus 70 bombers lost to enemy fire (4480 IC).
With these results, it's clear that Heavy Fighters are winning. Jets are the big losers here, with light fighters and rocket interceptors having comparable performance. Note that if we increased the guns on the rockets (say to +5), their number of bombers killed should go up, but their reliability drops to 25%. This could potentially double their accident losses, not necessarily giving them that much of an increase to their ratio. It's worth pointing out that the reliability increase for the Heavy Fighters from their design company really shines here, as adding guns is no big deal for them.
But what about escorted bombers? This is where things get ugly for, well, everyone. We'll give the RAF 500 escorting fighters. This should make the defenders perform much worse.
Against Rockets, this is what happens:
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The bombers only did 0.6 bomb damage to buildings, which is practically nothing. The rockets lost 450 planes to all causes (8100 IC) and shot down 119 fighters (3332 IC) and 60 bombers (3840 IC). That's much worse than earlier, and is no surprise. The Mustangs are basically killing them indiscriminately, while the bombers get their share.
Against Jets:
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The bombers did 2.7 building damage (worse, but not too serious). The jets lost 218 planes to all causes (6540 IC lost) to 172 escorts (4816 IC) and 31 STRs (1984 IC).
Against Heavy Fighters:
View attachment 395221
4.8 buildings damaged (that might cause concern given the fact that heavy fighters are involved and it's their damn job to stop these bombers). 188 heavy fighters lost to all causes (6016 IC) with 71 escorting fighters lost to enemy fire (1988 IC) and 53 STRs lost to enemy fire (3392 IC).
Against light fighters:
View attachment 395223
3.3 buildings damaged by the bombers. 192 light fighters lost to all causes (5376 IC) versus 177 escorting planes shot down (4956 IC) and 27 STRs killed (1728 IC).