So I found out during the Spore Lung Missions where the main lung is behind deep water and a destructible bridge, you can still destroy the lung with a hellbomb pack. We successfully did so after a brave patriot sacrificed themselves by activating the hellbomb and throwing themselves into the deep water moat.

Also... Love how the hellbombs will spawn on the outside but on top of the lung. A brave soul has to die so a helldiver can land on the surface and retrieve it.

Edit: Found the entrance. It's in the tunnel with the lung tube... Took 2 more missions to find it. Kept missing it.