And in the early days of nuclear weapons bombers dedicated to their delivery also often had heated bomb-bays to keep the device at a comfortable temperature, plus often a crawlway for some electee from the crew to physically enable the first PAL stage*. The last such design with both those features that occurs to me at the moment is the Douglas A3D & B-66 family.
* Even earlier than that was a crawl-way to the bomb-bay to enable the 'pit' to be pushed the final few inches into the casing.