As August and Shane have been quicker at the keyboard this morning on there takes, here is my 2 cents on the subject!
The first Canadian built Lancaster to be fitted with a Martin 250CE was aircraft number KB783 .This aircraft was sent to England for trials. The Martin turret was introduced on the production line on aircraft KB855.So of the 430 aircraft production run, 154 aircraft were fitted with the Frazer Nash mid upper turret.The remaining 276 were equipped with the Martin 250CE.
Only one Canadian Lancaster ,to be fitted with the Frazer Nash turret, KB839,survives at Greenwood Nova Scotia. You can still clearly see the turret location on the aircraft today
The change to the Martin turret involved not only the change in position due to weight and balance , but to the aircraft systems as well. The Martin turret was electrically operated while the earlier Frazer Nash was hydraulically operated. The aircraft's electrical system was changed to compensate for heavier electrical demand.
The change in mid upper turrets had also been mandated for the British built Lancasters at the same time, but other priorities had sidelined its introduction to later in the production run.
Interestingly Canadian Lancasters ,built at Malton Ontario,were built with turrets and without. Every fourth aircraft on the production line was built with turrets. On aircraft built without turrets, covers were fared over turret openings , and turrets were installed once the aircraft had been delivered to the UK. Maintenance Units located throughout the UK, took the aircraft on delivery from Canada and fitted the turrets. From the looks of the information the MU's at Kemble and St Athan did most of the turret fitting.
The main reason why this was done, was to ensure deliveries of aircraft were kept up to 6 Group in the UK. The Frazer Nash Turrets were built in the UK and shipped across the Atlantic , which had a certain element of risk , even by 1943/44.
I have yet to see any information(or list) on the which actual aircraft were delivered to UK with turrets or without. The Lancaster X was subject to a large number of modifications over the course of production, which ran from large items, like engines, turrets ,bomb doors and blisters to smaller items like electrical and rivets.
CWH did at one point during the restoration, have a Frazer Nash Mid upper turret, to install in FM213.As the pictures show, it was trial fitted. The work involved would have been significant and kept the aircraft on the ground longer.The Martin ring assembly was fitted shortly after FM213 flew after it restoration. As JDK mentioned, it is a great place to view from in flight !
I am not sure where the turret went, I didn't see it in the storage barn, last time I was in it.
KB839, you can just see were the turret ring is , just in front of beacon light and above the roundel position.
Martin 250CE installed on KB944 in Ottawa
MRP