v1.3:
I've managed to reduce the height even more, so now it can be carried on almost any plane. The small carrier plane now manages to take off and land with ease. Also it's engine power was increased a bit.
Beware there is a bug that when you enter the editor the first part you go into the settings of will be set back to the limitations of the settings panel, meaning that XML-modifications will be gone.
There are two ways to prevent this:
1. When entering the editor from the menu or after exiting a flight, click on an unmodded part (fuselage pieces, landing gear or wings for example) and go into it's settings first before proceeding to the props and engines.
2. When entering the editor from the menu or after exiting a flight, load the design a second time from the menu in the editor.

This is important when changing the Activation Groups of the torpedo, as it would resize the propellers and they would collide with parts of your plane, resulting in an explosion.

v1.2:
The design had some major issues when being launched from a carrier plane somehow, so I got my hands on it again.
It has gotten a very tiny bit longer and I have optimized weight and buoyancy distribution, also the main wings were moved further to the front for a more stable flight and touchdown.

I have also included my quick and dirty torpedo bomber which I now use for testing.
It has two modded miniguns and it flies very stable, but it's not very agile.
I haven't tried starting and landing with it yet, as I always start in the air, but it has a landing gear, so you might try it.
Edit: I have tried it now and you have to put a detacher between fuselage and nosewheel to make it work. Detach it before launching the torpedo, or they will collide. Landing is still possible with just the main landing gear.

The warhead still consists of four Bomb 25s and one Bomb 50 for a total of 1500 lbs, killing the USS Beast with one hit.

Optimal speed for launching is between 650 and 750 MPH (can be slower if the torpedo has enough time to accelerate to 700 MPH in the air), optimal height is 1000 feet ASL and below.
You should fly pretty much level when launching.

I haven't tested the speed of this version of the torpedo, but it should be between 230 and 260 MPH in water again and still ~700 MPH in the air.

AG1 is for launching and activating the engines of the torpedo, which react to throttle. (You can also bind the prop-engines to the VTOL-slider, if you want to have seperate throttle control for your aircraft/watercraft)
Throttle should be left at 100% the entire time from launch to hit.

Feel free to save the torpedo as a subassembly and equip your already existing and future crafts with it.

Enjoy! :)