tdracer,
Thanks for coming back.
Yes, I've seen these claims and, honestly, I am a bit sceptical. I don't know a single combat jet that didn't struggle with internal volume, and adding fairly large lumps on the outside (that definitely increase frontal area) without reducing drag seems unlikely. However, it's possible that the effects aren't as marked at subsonic speeds, as you mentioned. A change in desired sortie profiles can make big changes to both drag and fuel burn. It's also possible that the drag reduction claim includes the drag of external bombs - the F-15 combines conformal tanks with revised bomb carriage locations to reduce drag. (Interestingly, some of the F/A-18 proposals included a 'stealth' (probably also lower drag) weapons 'pod' on the centreline.
The other possibility, of course, is that the original airframe design wasn't worked as thoroughly as it might have been, and they found this extra volume later on, when the need drove them.
Incidentally, the Buccaneer belly tank on the S2B was originally designed as a solution to the excessive drag created when Blackburns looked at putting four more 1000lb bombs on the outside of the bomb bay door. They came up with the idea of adding a fairing on the outside of the door (which already had a fuel tank it, i believe) which would provide recesses for the bombs to lie in. The external bombs idea wasn't taken forward, but the belly tank provided a very efficient way of adding fuel.
Tough stuff, this pesky aerodynamics, ain't it?
Huge respect as always to those working the wind tunnels,
Engines