FF rockets are effective against ground targets and WWII era heavy bombers. However they weren't introduced into combat until 1945.
The Luftwaffe successfully used two rockets in the air to air role; the R4M and the WGr 21 which was known as the BR 21 when fired from aircraft.
The Luftwaffe introduced folding fin technology in the form of the 55mm diameter R4M rocket in late 1944/1945 and used them effectively against USAAF bomber formations. The R4M became the pattern for all allied and soviet post war unguided rockets.
Adolf Galland felt that the Me 262 and R4M was finally enough to defeat the bombers. He would know as he used them in combat. They were effective and relatively accurate though not as accurate as guns. The key breakthrough was their low dispersion compared to previous rockets. The folding fins gave higher accuracy due to a large fin area, as well as a practical and compact installation. They were simultaneously spin stabilised. Their falloff was comparable to the Mk108 canon. To be effective they needed to be aimed by a Lead computing gyro sight which in the German case was the EZ42. Unfortunately for a time the remotely mounted gyros were mounted incorrectly due to a installation manual deficiency causing the pilots to loose trust and rely on their marksmanship as aces. Fw 190s so equipped never went through the problem. The EZ42 had provision for introduction of a range only radar mounted in the leading edge that fed the EZ42 via a computer called Oberon but these additions never saw service.
The BR21, which was used from 1943 onwards, was based on the famous WGr 21 tube launched artillery rocket, the nebelwerfer (dyglycol powered since 1939). The technique was for a fighter formation to approach the target aircraft, a formation of B17 for instance, from behind and at a fixed range of about 1200m fire into the formation. The rockets warhead was set to detonate using a time fuse. Range was determined by the standard Revi gunsight which could determine range accurately from the known wingspan of the target bomber.
A squadron of Luftwaffe fighters might reckon to destroy 2 or 3 B-17 all without getting within fully effective range of the Bombers Brownings.
The appearance of escorts such as the P38 ended the success of this weapon as the relatively small German fighters were too cumbersome to operate in the presence of escorts while carrying this weapon.
A planed weapon was the R100 and R100 BS of which 25 were test fired with plans for production. This was a large supersonic 18cm unguided air to air rocket equipped either with a radar proximity fuse or in the BS version a timed shaped charge fuse which fired forward 400 incendiary shrapnel pellets. It was to be aimed by the same Oberon computer mentioned above however it was intended that at night the aiming would be by a conical scan radar then under development known as the FuG 244. An Arado 234P night fighter was intended to carry 3 of these.
The Luftwaffe nightfighter force, the Nachtjagt, was aiming for almost completely automated interception and firing with these weapons; telemetry injecting intercept data direct into the night fighter autopilot while Oberon took over final aiming and firing of both guns and rockets by radar.
A rocket, which appears to be a 75mm version of the R4M, known as the Fohn often appears in the literature as a rocket from which much was expected.
There was a great amount of German work in the early 1940s using spin stabilised tube launched rockets, some from revolver like magazines thereby producing a gun like rocket launcher that could be installed in the fuselage however the Luftwaffe was unsatisfied with the accuracy if these weapons.