According to 2 Group its Fortress I came with ash trays, carpet, padded walls and Thermos flasks. They did test climbs to 38,000 feet and bombed Cologne from 35,000 feet. One reason for releasing the B-17 to British service was to see how things went. Then the RAF tried flying the aircraft for long periods of time at over 30,000 feet, the result was "lots of useful lessons learnt" or less nicely "lots of equipment had trouble operating at the altitudes flown and temperatures encountered over the duration of the mission."
On 12 August 1941 the Luftwaffe managed to intercept one B-17 over Brest at 32,000 feet, showing altitude alone would not be enough and in any case all too often the aircraft was leaving contrails, very bad for raids with only 1 or 2 aircraft.
Total of 20 B-17C arrived, 4 in April, 15 in May and 1 in June 1941. Non combat losses in the period were on 22 June B-17C lost on air test, flew into cumulus cloud at 33,000 feet, all on board killed including 1 USAAF officer, on 3 July B-17C destroyed by fire during ground engine running tests, on 28 July B-17C structural failure in severe turbulence, again all on board killed. Michael Bowyer in his Book 2 Group RAF gives the operations log.
51 sorties on 17 strike days over 3 months, July to September 1941, no more than 4 sorties on any given strike day.
8 July, two attacked Wilhelmshaven Barracks 6x1100 pound HE, 1 had engine trouble and attacked Norderney Port 4x1100 pound HE
23 July, Berlin, all returned early, 2 due to contrails, 1 for an unknown reason, 90 squadron says bad weather.
24 July all 3 sorties attacked ships at Brest, 12x1100 pound HE.
26 July, to Hamburg, one abandoned due to weather, one dropped 4x1100 pound HE on Emden.
2 August, 1 bombed Kiel 4x1100 pounds HE, 1 abandoned due to joining the wrong formation, 1 bombed Borkum port 4x1100 pound HE, instead of Bremen, due to cloud.
6 August, 2 sorties attacked Brest port but 1 is described as jettisoning bombs, 8x1100 pound HE.
12 August, 3 attacked primary targets (but 2 of these bombed through cloud), De Kooy airfield, Emden port, Cologne industrial area, each attack 4x1100 pound HE, 1 abandoned due to engine trouble.
16 August, 2 abandoned strike of ships at Brest due to weather, (1 of which was intercepted and was lost attempting a crash landing in Britain, 3 killed, 1 injured, 3 safe.) 2 bombed Dusseldorf Industrial Area 8x1100 pound HE.
19 August, Dusseldorf Industrial Area, 1 abandoned due to contrails, 1 abandoned due to frozen guns.
21 August, Dusseldorf Industrial Area, 2 abandoned due to contrails (1 of these also had frozen guns), 1 abandoned due to supercharger problems.
29 August, Dusseldorf Industrial Area, 1 abandoned take off (so not considered a sortie), 1 abandoned due to contrails and engine trouble.
31 August, 1 attacked Bremen Industrial Area, 1 Spiekeroog port instead of Hamburg industrial area, 1 abandoned attack on Kiel due to supercharger problems, 4x1100 pound HE in each attack.
2 September, 1 bombed Bremen industrial area 4x1100 pounds HE, 1 abandoned due to contrails, 1 abandoned due to intercom problems (Duisberg and Hamburg rail targets)
4 September, 2 abandoned due to engine trouble but 1 of these bombed a secondary target, 1 abandoned due to intercom problems (Hamburg, Hannover, Essen industrial areas) Rotterdam port bombed 4x1100 pound HE.
6 September, 3 attacked Oslo shipyard 12x1100 pound HE, 1 abandoned with engine trouble.
8 September, Oslo shipyard, 2 lost (both shot down by fighters, all 14 crew killed), 2 abandoned due to weather (1 of these attacked by fighter), no bombs dropped.
15 September, Cologne industrial area, 1 abandoned due to contrails
16 September, Cologne industrial area, 1 abandoned due to engine problems.
20 September, Emden industrial area, 4x1100 pound HE
25 September, Emden industrial area, 1 abandoned due to contrails
51 sorties, 19 attacked the primary target, another 5 attacked other targets.
Some of the B-17C were sent to the Middle East and did a couple of sorties there, losing 2 B-17C to non combat reasons.
If Roger Freeman is correct in May 1944 the 8th Air Force 1st Division started a policy of removing the radio room gun and one waist gunner from its B-17s, mainly for centre of gravity reasons, both waist guns were retained though. In March 1945 the 381st group was flying without ball turrets, the 91st without waist guns or gunners, the 398th without chin turrets and the 94th without chin and ball turrets. The 398th liked the performance increase.
In June 1944 the 8th Air Force HQ gave permission to remove the ball turrets from its B-24s, it was a decision left to the groups so some removed the turret and others kept it.
Most successful gun positions on B-17 and B-24? remembering this is what the USAAF thought happened.