The Stirling was the only 4 engined bomber originally designed for 2 pilot operation. I believe that it maintained that set up throughout production, but stand to be corrected. Stirling squadrons in Bomber Command switched to single pilot operation along with other types in early 42.

Looking through some of the casualty lists - by late 1942/early 1943 most Stirling crews seemed to be single pilot.
Some of the earlier casualty lists with 2 Pilots listed had a navigator/observer,some did not have a navigator/observer listed.
Also as I posted above most Bomber Pilots did 1 or 2 'stooge' trips with an experienced skipper which woulkd show in a proportion of the losses.

Here's the 214 Sqdn Stirling loss site that pretty much verifies what you stated above. Most had one pilot and an FE even with the dual controls.

No. 214 (FMS) Squadron RAF - Crews and Losses - Stirling

Harris stated that his grand plan was to move the Stirlings and Halifaxes to Heavy Conversion Units (with crews completing a short Lancaster finishing school). However, in the 1942- early 43 timeframe, Lancasters were in short supply so he felt compelled to send them along on Ops (also including the Hampdens, Whitleys, and Wimpys still operational).

Should note that the Stirling could and did raid Italy as did Lancasters. Not sure about the Halifax.

Regarding the high number of OTU losses, the condition of the Wimpy's used in the OTUs were less than desirable with de-rated engines that, again form Peden's book, would give a foot and a half of altitude every 100 miles with undercart down and full flaps on overshoot. These same aircraft were sent on Ops.

Halibags did raid Italy, their ceiling was also higher than the Stirling. OTU Wimpys were usually earlier marks that were 'op expired' they did not receive the same maintenance as front line aircraft. They rarely carried out ops, aside of the Thousand Bomber raids, Nickels and a few other usually not to distant targets as a diversion. Aside of giving crews op experience, it wasn't sound economics to send newly trained crews out on ops in worn out aircraft. Harris once said of the Stirling: 'I can't send my crews/ young men out to die in an aircraft like that'. Unfortunately he had no choice until losses became prohibitive in late 43.

Interesting that Chris Barnes states in his 1967 Putnam that Shorts originally submitted a 112ft (Sunderland type) wing for their B.12/36 tender. which would have given a more capable performance:
" Unfortunately before ordering any prototypes ,the Air Ministry stipulated that the span must not exceed 100ft in order to conform to exiting hangar dimensions.; even this limitation was accepted by (Arthur) Gouge who increased the flap chord to 48 % of the wing chord and hoped to obtain Hercules VI engines in time for production."
This comment is repeated almost verbatim in Air Enthusiast No.10 in 1979, along with the " fitting in crates " story.
Later on in August 02 Aeroplane Monthly states that the 100ft span was an attempt to limit overall size and weight limitations for the then airfield capacities.

Thanks again all.

I can confirm that Halifaxes flew to Italy. For example 158 Squadron attacked Genoa on the 23 October 1942.

I found the Short Stirling Airfix instructions online that may have been the promotion of the hangar door rumour:
https://cimg3.ibsrv.net/gimg/pprune....96e740d6fc.jpg

My stepfather did a tour on 7 Squadron on the early Stirlings, he was convinced they were better performers than subsequent batches possibly as a result of the raid on Rochester disrupting the production line. He though that there might have been a change in wing incidence leading to a loss of performance. He hated the undercart and throttle management systems calling them a pilots nightmare.

Later in the war they were used on supply missions to drop kit to the resistance in France. Several were lost this way

Not just supply missions. The Stirling Mk IV could stake a claim to being the best allied airborne forces aircraft. It could carry more stores both internally and externally, drop more parachutists and tow heavier gliders than the Dakota. The Dakota only won on numbers available.