Editing Boeing B-17 Flying Fortress (section)

=== Luftwaffe attacks ===
[[File:B-17 Damage Cologne.jpg|thumb|B-17G ''43-38172'' of the 8th AF 398th BG 601st BS which was damaged on a bombing mission over [[Cologne]], Germany, on {{Nowrap|15 October}} 1944; the bombardier was killed.<ref>[http://www.398th.org/Images/Images_Aircraft_B-17/Aircraft/43-38172-3O-P_19441015_JBk.html "43-38172"]. ''398th.org''. Retrieved: 24 January 2012.</ref>]]
After examining wrecked B-17s and B-24s, Luftwaffe officers discovered that on average it took about 20 hits with [[MG 151 cannon|20 mm]] shells fired from the rear to bring them down.<ref name="AFM.76-9" /> Pilots of average ability hit the bombers with only about two percent of the rounds they fired, so to obtain 20 hits, the average pilot had to fire one thousand {{convert|20|mm|in|abbr=on}} rounds at a bomber.<ref name="AFM.76-9" /> Early versions of the Fw 190, one of the best German interceptor fighters, were equipped with two {{convert|20|mm|in|abbr=on}} [[MG FF cannon|MG FF]] cannons, which carried only 500 rounds when belt-fed (normally using 60-round [[drum magazine]]s in earlier installations), and later with the better Mauser MG 151/20 cannons, which had a longer effective range than the MG FF weapon. Later versions carried four or even six MG 151/20 cannon and twin [[MG 131 machine gun|13&nbsp;mm machine guns]]. The German fighters found that when attacking from the front, where fewer defensive guns were mounted (and where the pilot was exposed and not protected by armor as he was from the rear), it took only four or five hits to bring a bomber down.<ref name="AFM.76-9" />

To rectify the Fw 190's shortcomings, the number of cannons fitted was doubled to four, with a corresponding increase in the amount of ammunition carried, creating [[Focke-Wulf Fw 190 operational history#The Sturmböcke|the ''Sturmbock'']] bomber destroyer version. This type replaced the vulnerable twin-engine ''Zerstörer'' heavy fighters which could not survive interception by P-51 Mustangs flying well ahead of the combat boxes in an [[air supremacy]] role starting very early in 1944 to clear any Luftwaffe defensive fighters from the skies. By 1944, a further upgrade to [[Rheinmetall]]-[[Borsig]]'s {{convert|30|mm|in|abbr=on}} [[MK 108 cannon]]s mounted either in the wing, or in underwing, conformal mount gun pods, was made for the ''Sturmbock'' Focke-Wulfs as either the [[Rüstsatz|/R2 or /R8 field modification kits]], enabling aircraft to bring a bomber down with just a few hits.<ref name="AFM.76-9" />

The adoption of the [[21 cm Nebelwerfer 42|21 cm Nebelwerfer]]-derived ''[[Werfer-Granate 21]]'' (Wfr. Gr. 21) rocket mortar by the Luftwaffe in mid-August 1943 promised the introduction of a major "stand-off" style of offensive weapon&nbsp;– one strut-mounted tubular launcher was fixed under each wing panel on the Luftwaffe's single-engine fighters, and two under each wing panel of a few twin-engine [[Messerschmitt Bf 110|Bf 110]] daylight ''Zerstörer'' aircraft.<ref name="AFM.76-9" /> However, due to the slow 715&nbsp;mph velocity and characteristic [[Bullet drop|ballistic drop]] of the fired rocket (despite the usual mounting of the launcher at about 15° upward orientation), and the small number of fighters fitted with the weapons, the Wfr. Gr. 21 never had a major effect on the combat box formations of Fortresses.<ref name="AFM.76-9" /> The Luftwaffe also fitted heavy-caliber ''Bordkanone''-series 37, 50 and even {{convert|75|mm|in|sigfig=3|abbr=on}} cannon as anti-bomber weapons on twin-engine aircraft such as the special [[Junkers Ju 88|Ju 88P]] fighters, as well as one model of the [[Messerschmitt Me 410|Me 410]] ''Hornisse'' but these measures did not have much effect on the American strategic bomber offensive. The [[Messerschmitt Me 262|Me 262]], however, had moderate success against the B-17 late in the war. With its usual nose-mounted armament of four [[MK 108 cannon]]s, and with some examples later equipped with the [[R4M rocket]], launched from underwing racks, it could fire from outside the range of the bombers' {{convert|.50|in|mm|sigfig=3|abbr=on}} defensive guns and bring an aircraft down with one hit,<ref name="Schollars" /> as both the MK 108's shells and the R4M's warheads were filled with the "shattering" force of the strongly [[Brisance|brisant]] [[RDX|Hexogen]] military explosive.