"I read an interesting article about the Lanc a while ago. The Lanc would have been about 50 mph faster without any turrets and their associated weight, ammo, drag etc. Plus it would have had two less crew. Someone far cleverer than me (that's everyone then) applied their statistical minds to it and worked out that far less Lancs and crew would have been lost had it been produced sans turrets."
..and this of course was the crew used for the Vulcan (co-pilot replaced the FE and the BA renamed as "radar nav") where speed and height precluded the need for self defence. The problem with "de-arming" the Lanc was that it was felt that the weight saving would not be used for height and speed but to carry extra fuel and weapons load as in the late war "specials". Another thought was to remove the guns/ammunition and just to have look-out positions (akin to the later Shackletons) as good lookout probably saved more aircraft than shooting down an attacker, bearing in mind that the Lanc had .303 MG compared to the night-fighters' 20mm cannon.