Look at how Russia uses their old heavy bombers for an idea: they use them to carry missiles that can be released outside of air defense range. The larger plane

Look at how Russia uses their old heavy bombers for an idea: they use them to carry missiles that can be released outside of air defense range. The larger plane reduces the fuel required by the missile (meaning more explosives) and allows the missiles to be positioned and fired faster than a truck or ship can get into position. The idea of flying over the target is kind of old - modern glide bombs (again, use the aircraft's energy instead of reducing payload) have a 20-50km range and are more accurate. The super expensive stealth bomber lets you move into a very unexpected position and release missiles/glide bombs in a way that may not allow for any air defense work at all.