[JoeB]

Just to benchmark the SBD in a primary source, the "Aircraft Characteristics and Performance" sheets for SBD-5 dated June 1 1944 give the a/c's range with 1000# bomb as 1115 statute miles, radius 240, same nominal range but 260 mile radius with 500#. The conditions for the radius are specified in detail, including warm up, take off, forming up, cruise, combat, return, reserves, etc. (the sheets I have for earlier SBD's don't give radius). It's a bit different than you quoted but same idea of a quite small %, and it's considerably affected by the assumptions. (editing to add, those figures assume full internal fuel load plus the bomb).

AFAIK the USN didn't officially specify combat radius on pre-WWII types like the SBU, and as you know SOC was usually employed as a cruiser floatplane during WWII, though it could also operate on conventional landing gear. The problem with directly extrapolating the radius/range as a % is that parts of the assumed fuel consumption like warm up, form up, and particularly end of flight reserves are constant: a short enough legged plane would theoretically have a zero combat radius because it used up all the fuel doing those things and had none to cruise out to a target.

A less extreme real version is the official combat radius for the F4F-4 with no drop tank, as given in its ACP of July 1 1943: only 105 statute mile radius despite max range of 830. Part of this was also the assumption of much longer time at combat power for a fighter (20 min v 5 min for the SBD-5) but it's also the effect of the fixed components of consumption taken out of a lower max range. OTOH Lundstrom said in "The First Team" that the F4F pre-drop tanks was viewed by the operating units as having a practical radius of around 175 miles.

But even based on the latter figure, it wouldn't seem that SBU (548 st mile range in Swanborough/Bowers "USN A/c Since 1911") or SOC (675 miles same source) had a practical combat radius near to 200 miles. In an extraordinary situation with target location well known, smaller formation (or single SOC from a cruiser, perhaps), important enough to accept more risk of fuel exhaustion loss, maybe?

Joe