I was wondering…what about a 16" gun (or an 18"…or 20"…hell, go all Texas sized and go with a 24" gun)? They could only fire shells weighing 2000-3000 lbs, true, and the shock would probably break the bomb, but what if you made a shorter barrel and used an air cannon design with the subs ballast tanks as the accumulator? You’d only need to fire the thing a couple hundred feet into the air over, say, New York, to get an air burst.
Be kind of hard on the crew, but I think you could do it, depending on if you could slim down the bomb a bit at the same time you hardened it for the shock and designed a gun that could fire the thing without breaking it. It’s got a real Rube Goldberg-esqe feel that I like as well…
The X-Craft were towed behind full sized submarines until they were relatively close to the target.
Granted, that would make going through the heavily patrolled Atlantic an iffy proposition, but if they’d go all the way to develop an atomic bomb and decided sub delivery was the thing it wouldn’t take that much effort to attach the mini submarine directly to the mothership instead of towing.
It could also be a rather oversized version of the Chariot manned torpedos, easier to build and easier to elope.
When the Manhattan Project first started they didn’t know for sure how big or heavy the A-Bomb was going to be, but they figured it wasn’t going to be small or light. Initially they were planning on having to deliver it to an enemy harbor by a ship of some kind (unmanned).
What if you just put the bomb inside a normal freighter of something like rubber or rice or uniforms,
Set the timer, then let the boat be captured?
Not guaranteed to reach port, but what are the chances that the boat would be fully searched for a nuke before being taken somewhere it could do major damage?
4400kg is pretty small in relation to a full size freighter.
Which is not to imply the Nazis could have, as a practical matter, gotten far enough in the design process to have actually built one before the fall of Berlin. But the concept is sound and they functioned as intended.
However, while I personally would like to avoid having a 15 kiloton nuclear weapon fired at me, as a one shot weapon of war it’s really rather lackluster. Certainly not the sort of thing which would inflict damage equivalent to what was done to Germany with conventional weapons.
This reminds me of some of the ridiculous theories that were being proposed a few years back about the Port Chicago disaster. I think we even had a thread here at one point about it. The scientists at Los Alamos did use what data they could get from the incident to help them get a feel for how an atomic bomb explosion might behave in a port situation.