Wellington and both Liberators have Excellent Endurance so that is a common denominator here. I really like the Wellington and see it used. I would not like to see it totally bookmarked. But I think 7 will work. That ASW 4/5 is definitely pushing power creep though.
I forget the dividing line for number of MGs for Light vs "full" Defensive Armament. Was it 9 or 10? Do you have a link for the specifications that are unique to the GR Mk III? I have only been able to find stats for the "generic" B-24D that it was based on. I have found some of the modifications for radar, leigh light, etc, but nothing about how that changed the basic load-out and performance of the aircraft.
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Here is an interesting chapter on the Canadian B-24s. It says the Canadians removed one of the bomb bays and replaced it with fuel tanks to extend the range. I am not sure if that halves the bomb carrying capacity or not. The number of guns is a little confusing. One in the nose, "two in each waist position," four in the rear turret and two in the dorsal turret. The "two in each waist position" is not clear to me. Is that one on each side of the fuselage or two on each side? I think they just had one on each side. If so then that is 9 guns. Installing a two-gun turret in nose later on would give it the 10 guns usually reported.
So you are correct about 9 guns which means we can "downgrade" a bit to Light Defensive Armament. That makes me feel a little better about a cost of 7. It just seems weird to me that the "tank of air" would get Light Defensive Armament. But I get that they were stripping down to save weight and extend range out into the Atlantic. In fact, the reference says they even removed some armor.
So 9 MGs, 2700 lbs of bombs, and Light Defensive Armament. I will make the changes.
Wellington and both Liberators have Excellent Endurance so that is a common denominator here. I really like the Wellington and see it used. I would not like to see it totally bookmarked. But I think 7 will work. That ASW 4/5 is definitely pushing power creep though.